Water Online Test 8th Science Lesson 18 Questions in English
Water Online Test 8th Science Lesson 18 Questions in English
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Question 1 of 90
1. Question
- Assertion (A): Two-third of the planet Earth is filled with water.
Reasoning (R): Water exists in solid and liquid states only.
Correct
Explanation
Three fourths of our planet earth is filled with water. Water exists in three states namely solid, liquid and gas.
Incorrect
Explanation
Three fourths of our planet earth is filled with water. Water exists in three states namely solid, liquid and gas.
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Question 2 of 90
2. Question
- Which is the major water source in the surface of earth?
Correct
Explanation
Water on the surface of the earth is found mainly in oceans (97.25%), polar ice caps and glaciers (2.05%) and the remaining is in lakes, rivers and aquifers – ground water.
Incorrect
Explanation
Water on the surface of the earth is found mainly in oceans (97.25%), polar ice caps and glaciers (2.05%) and the remaining is in lakes, rivers and aquifers – ground water.
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Question 3 of 90
3. Question
- Choose the Incorrect statements.
i) The Chemical name of water is di hydrogen monoxide.
ii) Water can be broken into hydrogen and oxygen molecules.
iii) Water is chemically an unstable compound.
Correct
Explanation
Even our body is made up of 65% of water but it is not apparent. Water is a chemically stable compound. Its chemical name is di hydrogen monoxide (H2O). It can be broken up into hydrogen (H2) and oxygen (O2) when an electrical current is passed through it.
Incorrect
Explanation
Even our body is made up of 65% of water but it is not apparent. Water is a chemically stable compound. Its chemical name is di hydrogen monoxide (H2O). It can be broken up into hydrogen (H2) and oxygen (O2) when an electrical current is passed through it.
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Question 4 of 90
4. Question
- What is the name of the process using electric current to break down the water molecules?
Correct
Explanation
The process of breaking down of water molecules by the passage of electric current is known as electrolysis of water.
Incorrect
Explanation
The process of breaking down of water molecules by the passage of electric current is known as electrolysis of water.
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Question 5 of 90
5. Question
- Which of these electrodes are used in the electrolysis process of water?
Correct
Explanation
Electrolysis of water can be easily demonstrated with the help of an experiment. In this experimental set up, a glass beaker is fixed with two carbon electrodes and it is filled with water up to one third of its volume. The positive carbon electrode acts as anode and the negative carbon electrode acts as cathode.
Incorrect
Explanation
Electrolysis of water can be easily demonstrated with the help of an experiment. In this experimental set up, a glass beaker is fixed with two carbon electrodes and it is filled with water up to one third of its volume. The positive carbon electrode acts as anode and the negative carbon electrode acts as cathode.
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Question 6 of 90
6. Question
- Which of these is collected in the cathode of the electrolysis experiment?
Correct
Explanation
The electrodes are connected to a battery and current is passed until the test tubes are filled with a particular gas. If the gas collected is tested using a burning splint we can notice that the gas in cathode side burns with a popping sound when the burning splint is brought near the mouth of the test tube. This property is usually shown by hydrogen gas and so it is confirmed that the gas inside the test tube is hydrogen.
Incorrect
Explanation
The electrodes are connected to a battery and current is passed until the test tubes are filled with a particular gas. If the gas collected is tested using a burning splint we can notice that the gas in cathode side burns with a popping sound when the burning splint is brought near the mouth of the test tube. This property is usually shown by hydrogen gas and so it is confirmed that the gas inside the test tube is hydrogen.
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Question 7 of 90
7. Question
- Which of these gas burns brightly?
Correct
Explanation
The burning splint placed near the anode side burns more brightly confirming that it is oxygen gas.
Incorrect
Explanation
The burning splint placed near the anode side burns more brightly confirming that it is oxygen gas.
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Question 8 of 90
8. Question
- Assertion (A): The Hydrogen and oxygen ratio of water is 1:2.
Reasoning (R): Every two volumes of hydrogen there is one volume of oxygen in water.
Correct
Explanation
The ratio of hydrogen and oxygen is 2:1. Hence, for every two volumes of hydrogen collected at the cathode, there is one volume of oxygen collected at the anode.
Incorrect
Explanation
The ratio of hydrogen and oxygen is 2:1. Hence, for every two volumes of hydrogen collected at the cathode, there is one volume of oxygen collected at the anode.
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Question 9 of 90
9. Question
- Name the scientist who chemically prepared the water?
Correct
Explanation
Water was first prepared in 1781 by an English scientist Henry Cavendish. He discovered hydrogen gas when active metals reacted with Sulphuric acid. The hydrogen gas released was highly inflammable and burnt to form a colorless product called water.
Incorrect
Explanation
Water was first prepared in 1781 by an English scientist Henry Cavendish. He discovered hydrogen gas when active metals reacted with Sulphuric acid. The hydrogen gas released was highly inflammable and burnt to form a colorless product called water.
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Question 10 of 90
10. Question
- Which of this process also produces water chemically?
Correct
Explanation
Water is also produced by the reduction of metal oxide by hydrogen, burning of hydrogen in air and burning of hydrocarbons in air. Respiration of plants and animals also releases water.
Incorrect
Explanation
Water is also produced by the reduction of metal oxide by hydrogen, burning of hydrogen in air and burning of hydrocarbons in air. Respiration of plants and animals also releases water.
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Question 11 of 90
11. Question
- Choose the correct statements about the Henry Cavendish.
i) Discovered hydrogen and called it as inflammable air.
ii) Metals and strong acids were mixed to create hydrogen.
iii) Metals and strong bases were mixed to create carbon dioxide.
Correct
Explanation
Henry Cavendish was a British philosopher, scientist, chemist, and physicist. Cavendish is noted for his discovery of hydrogen. He called it inflammable air. He mixed metals with strong acids and created hydrogen. He created carbon dioxide also by combining metals with strong bases.
Incorrect
Explanation
Henry Cavendish was a British philosopher, scientist, chemist, and physicist. Cavendish is noted for his discovery of hydrogen. He called it inflammable air. He mixed metals with strong acids and created hydrogen. He created carbon dioxide also by combining metals with strong bases.
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Question 12 of 90
12. Question
- Which of these statements are not true regarding the laboratory preparation of water?
Correct
Explanation
The apparatus used for the preparation of water in the laboratories. In this method, pure hydrogen gas is passed through anhydrous calcium chloride to absorb water vapor, if present. Dry hydrogen coming out of the opening is burnt with sufficient supply of air. The burnt hydrogen gas forms droplets of water, when it comes in contact with the cold flask. Distilled water without any dissolved matter is obtained by this method.
Incorrect
Explanation
The apparatus used for the preparation of water in the laboratories. In this method, pure hydrogen gas is passed through anhydrous calcium chloride to absorb water vapor, if present. Dry hydrogen coming out of the opening is burnt with sufficient supply of air. The burnt hydrogen gas forms droplets of water, when it comes in contact with the cold flask. Distilled water without any dissolved matter is obtained by this method.
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Question 13 of 90
13. Question
- Which is not a property of nature pure water?
Correct
Explanation
Nature Pure water is a clear and transparent liquid. It is colorless, odorless and tasteless.
Incorrect
Explanation
Nature Pure water is a clear and transparent liquid. It is colorless, odorless and tasteless.
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Question 14 of 90
14. Question
- Assertion (A): The boiling point of water is 100°C at atmospheric pressure.
Reasoning (R): The water boils and changes to steam in the boiling point.
Correct
Explanation
The boiling point of water is 100°C at atmospheric pressure. At this temperature, water boils and changes to steam.
Incorrect
Explanation
The boiling point of water is 100°C at atmospheric pressure. At this temperature, water boils and changes to steam.
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Question 15 of 90
15. Question
- Which of these increases the boiling point of the water?
Correct
Explanation
The boiling point of water increases with increase in pressure. For example, when a pressure cooker is heated, a high pressure is built inside it. The high pressure increases the boiling point of water. Thus water remains a liquid at a higher temperature (> 100°C) in the cooker. This cooks the food faster.
Incorrect
Explanation
The boiling point of water increases with increase in pressure. For example, when a pressure cooker is heated, a high pressure is built inside it. The high pressure increases the boiling point of water. Thus water remains a liquid at a higher temperature (> 100°C) in the cooker. This cooks the food faster.
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Question 16 of 90
16. Question
- Which of these is not a physical property of pure water?
Correct
Explanation
Pure water has the following physical properties.
- Pure water boils at 100° C at one atmospheric pressure.
- Pure water freezes at exactly 0°C at one atmospheric pressure.
- Pure water has a density of 1 gm/cm3
Incorrect
Explanation
Pure water has the following physical properties.
- Pure water boils at 100° C at one atmospheric pressure.
- Pure water freezes at exactly 0°C at one atmospheric pressure.
- Pure water has a density of 1 gm/cm3
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Question 17 of 90
17. Question
- Choose the correct statements about the freezing point of water.
i) The freezing point of water is 0°C.
ii) The freezing point of water increases with increase in pressure.
Correct
Explanation
Water freezes at 0°C and forms ice. Thus, the freezing point of water is 0°C. The freezing point of water decreases with increase in pressure.
Incorrect
Explanation
Water freezes at 0°C and forms ice. Thus, the freezing point of water is 0°C. The freezing point of water decreases with increase in pressure.
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Question 18 of 90
18. Question
- Which of the following statement is not true?
Correct
Explanation
When the skaters move on ice, they exert pressure on it. This pressure lowers the freezing point. As a result, the ice melts underneath the skate and allows the skaters to glide across the ice with little effort. When the skaters move forward pressure is decreased and the water re-freezes to ice again.
Incorrect
Explanation
When the skaters move on ice, they exert pressure on it. This pressure lowers the freezing point. As a result, the ice melts underneath the skate and allows the skaters to glide across the ice with little effort. When the skaters move forward pressure is decreased and the water re-freezes to ice again.
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Question 19 of 90
19. Question
- Which of this statement is true regarding the frozen ice cubes and water?
Correct
Explanation
When ice cubes are put in a glass of water at room temperature, they float on the surface of the water. This is because ice is lighter than water. It means that the density of ice is lower than that of water.
Incorrect
Explanation
When ice cubes are put in a glass of water at room temperature, they float on the surface of the water. This is because ice is lighter than water. It means that the density of ice is lower than that of water.
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Question 20 of 90
20. Question
- Choose the Incorrect statements.
i) Ice is a good conductor of heat.
ii) In 0°C water below the frozen ice remains in liquid form.
iii) The water below the frozen ice is used for the survival of the aquatic life.
Correct
Explanation
When the winter temperature is below 0°C, the water in the lake will start freezing. The frozen ice will float at the top and cover the lake. Since ice is a bad conductor of heat it does not allow heat to pass through it. So, the water below the ice remains in liquid form, where most of the aquatic life lives. This enables the aquatic animals and plants to survive even in extreme cold conditions.
Incorrect
Explanation
When the winter temperature is below 0°C, the water in the lake will start freezing. The frozen ice will float at the top and cover the lake. Since ice is a bad conductor of heat it does not allow heat to pass through it. So, the water below the ice remains in liquid form, where most of the aquatic life lives. This enables the aquatic animals and plants to survive even in extreme cold conditions.
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Question 21 of 90
21. Question
- What is the density of water at 4°C?
Correct
Explanation
Density of water at different temperature
Incorrect
Explanation
Density of water at different temperature

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Question 22 of 90
22. Question
- Which is an unusual property of water?
Correct
Explanation
For the same mass of ice and of water, the volume of ice is more than that of water. It is an unusual physical property of water. In the Himalayas the temperature can go down even below 0°C. The water in the water pipes will freeze at this temperature to ice. If the pipes are not strong they can crack, develop leaks or even burst. This is because freezing of water will cause an expansion in the volume.
Incorrect
Explanation
For the same mass of ice and of water, the volume of ice is more than that of water. It is an unusual physical property of water. In the Himalayas the temperature can go down even below 0°C. The water in the water pipes will freeze at this temperature to ice. If the pipes are not strong they can crack, develop leaks or even burst. This is because freezing of water will cause an expansion in the volume.
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Question 23 of 90
23. Question
- Assertion (A): A thermometer does not register any temperature variation if an ice cube is heated.
Reasoning (R): The heat energy is utilized by the state of change from solid to liquid.
Correct
Explanation
Latent heat of fusion of ice: If ice cubes are heated in a beaker in which a thermometer is placed, the thermometer does not register any rise in temperature till all the ice melts. The question arises where the heat energy goes if there is no rise in temperature. The heat energy is utilized in changing the state of ice from solid to liquid.
Incorrect
Explanation
Latent heat of fusion of ice: If ice cubes are heated in a beaker in which a thermometer is placed, the thermometer does not register any rise in temperature till all the ice melts. The question arises where the heat energy goes if there is no rise in temperature. The heat energy is utilized in changing the state of ice from solid to liquid.
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Question 24 of 90
24. Question
- Which of these have the highest latent heat of fusion?
Correct
Explanation
The amount of heat energy required by ice to change into water is called latent heat of fusion of ice. Ice has the highest latent heat of fusion, i.e., 80 calories/g. or 336 J/g.
Incorrect
Explanation
The amount of heat energy required by ice to change into water is called latent heat of fusion of ice. Ice has the highest latent heat of fusion, i.e., 80 calories/g. or 336 J/g.
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Question 25 of 90
25. Question
- Assertion (A): Ice is used to maintain the freshness of the food for longer time.
Reasoning (R): The high latent heat fusion value of ice absorbs the heat from the food when it melts.
Correct
Explanation
The freshness of fish and meat can be maintained by placing them in contact with ice. With its larger latent heat, ice is able to absorb a large quantity of heat from the fish as it melts. Thus, food can be kept at a low temperature for an extended period of time.
Incorrect
Explanation
The freshness of fish and meat can be maintained by placing them in contact with ice. With its larger latent heat, ice is able to absorb a large quantity of heat from the fish as it melts. Thus, food can be kept at a low temperature for an extended period of time.
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Question 26 of 90
26. Question
- Which of these have the highest latent heat of vaporization value?
Correct
Explanation
Latent heat of vaporization of water
When water attains the temperature of 100°C, it starts changing its state from liquid to gaseous state. However, the temperature of water does not rise above 100°C. It is because the supplied heat energy only changes the state of the boiling water. This heat energy is stored in steam and is commonly called latent heat of vaporization of steam. The steam has the highest latent heat of vaporization and its value is 540 calories/g or 2268 J/g.
Incorrect
Explanation
Latent heat of vaporization of water
When water attains the temperature of 100°C, it starts changing its state from liquid to gaseous state. However, the temperature of water does not rise above 100°C. It is because the supplied heat energy only changes the state of the boiling water. This heat energy is stored in steam and is commonly called latent heat of vaporization of steam. The steam has the highest latent heat of vaporization and its value is 540 calories/g or 2268 J/g.
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Question 27 of 90
27. Question
- Which of these property of water takes time to become hot or cold?
Correct
Explanation
Specific heat capacity: The amount of heat that is needed to raise the temperature of a unit mass of a substance by 1°C is called specific heat capacity of that substance. The specific heat capacity of water is very high. One gram of water requires 1 calorie of heat to raise its temperature by 1°C. Due to its high specific heat capacity, water takes time to become hot as well as to cool down. Thus, water can absorb a lot of heat and retain it for a longer time.
Incorrect
Explanation
Specific heat capacity: The amount of heat that is needed to raise the temperature of a unit mass of a substance by 1°C is called specific heat capacity of that substance. The specific heat capacity of water is very high. One gram of water requires 1 calorie of heat to raise its temperature by 1°C. Due to its high specific heat capacity, water takes time to become hot as well as to cool down. Thus, water can absorb a lot of heat and retain it for a longer time.
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Question 28 of 90
28. Question
- Which of these mechanisms use the specific heat capacity property of water?
Correct
Explanation
The property of specific heat capacity of water is used to cool engines. Water is circulated around car engine using the radiator pump and the heat is absorbed. Thus the engine is protected from getting too hot.
Incorrect
Explanation
The property of specific heat capacity of water is used to cool engines. Water is circulated around car engine using the radiator pump and the heat is absorbed. Thus the engine is protected from getting too hot.
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Question 29 of 90
29. Question
- Which form of water does not react with litmus paper?
Correct
Explanation
Pure water is neutral and it shows no action towards litmus paper.
Incorrect
Explanation
Pure water is neutral and it shows no action towards litmus paper.
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Question 30 of 90
30. Question
- At which of this temperature the water decomposes to form hydrogen and oxygen gas?
Correct
Explanation
Water is a very stable compound. It does not decompose into elements, when heated to ordinary temperatures. However, if it is heated to 2000°C, 0.02% of water decomposes to form hydrogen and oxygen gas.
Incorrect
Explanation
Water is a very stable compound. It does not decompose into elements, when heated to ordinary temperatures. However, if it is heated to 2000°C, 0.02% of water decomposes to form hydrogen and oxygen gas.
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Question 31 of 90
31. Question
- Assertion (A): Hydrogen with water traces react with sunlight and cause explosion to produce hydrogen chloride.
Reasoning (R): Dry hydrogen and chlorine gases do not react in the presence of Sunlight.
Correct
Explanation
Water acts as a catalyst in a number of reactions. Perfectly dry hydrogen and chlorine gases do not react in the presence of sunlight. However in the presence of traces of water, the reaction takes place with explosion to produce hydrogen chloride.
Incorrect
Explanation
Water acts as a catalyst in a number of reactions. Perfectly dry hydrogen and chlorine gases do not react in the presence of sunlight. However in the presence of traces of water, the reaction takes place with explosion to produce hydrogen chloride.
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Question 32 of 90
32. Question
- Which of these metals does not react vigorously with water at room temperature?
Correct
Explanation
Water reacts with some metals. Metals such as sodium, potassium and calcium react vigorously with water at room temperature.
Incorrect
Explanation
Water reacts with some metals. Metals such as sodium, potassium and calcium react vigorously with water at room temperature.
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Question 33 of 90
33. Question
- In which of this reaction the hydrogen gas burns due to the heat?
Correct
Explanation
Sodium reacts with water to form hydrogen gas and sodium hydroxide solution. Due to the heat evolved in this reaction the hydrogen (gas) catches fire and burns.
2Na + 2H2O 2NaOH + H2
Incorrect
Explanation
Sodium reacts with water to form hydrogen gas and sodium hydroxide solution. Due to the heat evolved in this reaction the hydrogen (gas) catches fire and burns.
2Na + 2H2O 2NaOH + H2
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Question 34 of 90
34. Question
- What is the chemical reaction of magnesium and hot water?
Correct
Explanation
Magnesium is little more sluggish. It reacts with hot water and gives hydrogen and magnesium hydroxide solution.
2Mg + 2H2O Mg(OH)2 + H2
Incorrect
Explanation
Magnesium is little more sluggish. It reacts with hot water and gives hydrogen and magnesium hydroxide solution.
2Mg + 2H2O Mg(OH)2 + H2
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Question 35 of 90
35. Question
- Choose the correct statements.
- i) Iron is the only metal which forms iron oxide with water called as rust.
- ii) Corrosion is an immediate process of iron rusting.
iii) Iron is used to construct buildings, factories, bridges and vehicles.
Correct
Explanation
Many other metals react with water to form oxides and hydroxides. Iron is one such metal which forms iron oxide, called rust. Iron is used in many buildings, factories, bridges, ships and vehicles. The slow and gradual rusting of iron is called corrosion.
Incorrect
Explanation
Many other metals react with water to form oxides and hydroxides. Iron is one such metal which forms iron oxide, called rust. Iron is used in many buildings, factories, bridges, ships and vehicles. The slow and gradual rusting of iron is called corrosion.
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Question 36 of 90
36. Question
- Assertion (A): Copper is mostly used for making pipes and boilers.
Reasoning (R): Copper does not react with water at any temperature.
Correct
Explanation
Copper does not react with water at any temperature. That is why it is used for making pipes and boilers.
Incorrect
Explanation
Copper does not react with water at any temperature. That is why it is used for making pipes and boilers.
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Question 37 of 90
37. Question
- Which of these dissolves in water and produces hydrochloric acid?
Correct
Explanation
Chlorine gas dissolves in water and produces hydrochloric acid.
2Cl2 + 2H2O Sunlight 4HCl + O2
Incorrect
Explanation
Chlorine gas dissolves in water and produces hydrochloric acid.
2Cl2 + 2H2O Sunlight 4HCl + O2
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Question 38 of 90
38. Question
- Name the substance which dissolves other molecules and compounds?
Correct
Explanation
A solvent is a substance which dissolves other molecules and compounds. For example, in a salt solution, water is the solvent and salt is the solute.
Incorrect
Explanation
A solvent is a substance which dissolves other molecules and compounds. For example, in a salt solution, water is the solvent and salt is the solute.
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Question 39 of 90
39. Question
- Choose the correct statements.
- i) Water is called as the Universal solute.
- ii) Water has the unique property of dissolving more substances than any other liquids.
iii) Water dissolves only solid substances like salt and sugar.
- a) i only
- b) ii only
- c) iii only
- d) All the above
Explanation
Water has a unique property to dissolve more substances than any other liquids. It can dissolve solids such as salt and sugar, liquids such as honey and milk and gases such as oxygen and carbon dioxide in it. Water can dissolve more number of substances than any other solvent. Therefore, it is called as universal solvent.
- Choose the correct statements.
- i) Water is called as the Universal solute.
- ii) Water has the unique property of dissolving more substances than any other liquids.
iii) Water dissolves only solid substances like salt and sugar.
Correct
Explanation
Water has a unique property to dissolve more substances than any other liquids. It can dissolve solids such as salt and sugar, liquids such as honey and milk and gases such as oxygen and carbon dioxide in it. Water can dissolve more number of substances than any other solvent. Therefore, it is called as universal solvent.
Incorrect
Explanation
Water has a unique property to dissolve more substances than any other liquids. It can dissolve solids such as salt and sugar, liquids such as honey and milk and gases such as oxygen and carbon dioxide in it. Water can dissolve more number of substances than any other solvent. Therefore, it is called as universal solvent.
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Question 40 of 90
40. Question
- Which of these is the reason for the concentric rings in evaporated water?
Correct
Explanation
You can see a number of concentric rings of solid matter deposited on the watch glass. These are the dissolved solids left behind after the evaporation of water. Salts, minerals and impurities are the solids dissolved in water.
Incorrect
Explanation
You can see a number of concentric rings of solid matter deposited on the watch glass. These are the dissolved solids left behind after the evaporation of water. Salts, minerals and impurities are the solids dissolved in water.
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Question 41 of 90
41. Question
- Which of these is not true regarding the dissolved salts in water?
Correct
Explanation
Dissolved salts are important for the following reasons.
- They are essential for the growth and development of plants.
- They add taste to water.
- They supply the essential minerals needed for our bodies.
- Most of the chemical reactions important for our living take place in the cells of our body with the help of water.
Incorrect
Explanation
Dissolved salts are important for the following reasons.
- They are essential for the growth and development of plants.
- They add taste to water.
- They supply the essential minerals needed for our bodies.
- Most of the chemical reactions important for our living take place in the cells of our body with the help of water.
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Question 42 of 90
42. Question
- Choose the correct statements.
i) River water and tap water forms concentric rings after evaporation.
ii) Rain water and the distilled water do not contain any salts.
iii) River water, tap water and well water contains dissolved salts.
Correct
Explanation
Tap water, river water and well water contain dissolved solids but rainwater and distilled water does not contain dissolved solids. Hence concentric rings are not formed in the rain water and distilled water after evaporation.
Incorrect
Explanation
Tap water, river water and well water contain dissolved solids but rainwater and distilled water does not contain dissolved solids. Hence concentric rings are not formed in the rain water and distilled water after evaporation.
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Question 43 of 90
43. Question
- Assertion (A): Air is present in the dissolved state in fresh water sources only.
Reasoning (R): Dissolved air is used for living organisms and the aquatic plants.
Correct
Explanation
Apart from solids and minerals, air is also dissolved in water. Air is present in dissolved state in all natural sources of water.
Incorrect
Explanation
Apart from solids and minerals, air is also dissolved in water. Air is present in dissolved state in all natural sources of water.
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Question 44 of 90
44. Question
- What is the approximate percentage of dissolved oxygen in water?
Correct
Explanation
The solubility of oxygen in water is higher than the solubility of nitrogen. Air dissolved in water contains approximately 35.6% oxygen along with nitrogen and carbon dioxide.
Incorrect
Explanation
The solubility of oxygen in water is higher than the solubility of nitrogen. Air dissolved in water contains approximately 35.6% oxygen along with nitrogen and carbon dioxide.
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Question 45 of 90
45. Question
- List the importance of air dissolved in water.
i) Important for the living organisms in water.
ii) Aquatic plants use dissolved carbon dioxide for photosynthesis.
Correct
Explanation
Air being dissolved in water is important for the following reasons.
- Air dissolved in water is important for the living organisms to survive.
- Fish extracts the oxygen from the water and expels water through the gills. Fish can survive in water only through the dissolved oxygen present in water.
- Aquatic plants make use of dissolved carbon dioxide for photosynthesis.
Incorrect
Explanation
Air being dissolved in water is important for the following reasons.
- Air dissolved in water is important for the living organisms to survive.
- Fish extracts the oxygen from the water and expels water through the gills. Fish can survive in water only through the dissolved oxygen present in water.
- Aquatic plants make use of dissolved carbon dioxide for photosynthesis.
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Question 46 of 90
46. Question
- Which of these react with the limestone and forms calcium bicarbonate?
Correct
Explanation
Carbon dioxide dissolved in water reacts with limestone to form calcium bicarbonate. Marine organisms such as snails, oysters, etc., extract calcium carbonate from calcium bicarbonate to build their shells.
Incorrect
Explanation
Carbon dioxide dissolved in water reacts with limestone to form calcium bicarbonate. Marine organisms such as snails, oysters, etc., extract calcium carbonate from calcium bicarbonate to build their shells.
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Question 47 of 90
47. Question
- Choose the Incorrect statements.
i) Dead sea has a single source of water which is connected to the sea.
ii) The water salinity is more than in the Dead Sea.
iii) Marine life is not possible in the Dead Sea due to the steady increase in the salinity.
Correct
Explanation
The salinity of water is more in the Dead Sea. It is actually a salt lake as it has a single source of water and is not connected to the ocean. It is landlocked and this causes the water to evaporate. This has led to a steady increase in its degree of salinity. Now the salinity is so high such that the marine life cannot survive in it. This is why it is called the Dead Sea.
Incorrect
Explanation
The salinity of water is more in the Dead Sea. It is actually a salt lake as it has a single source of water and is not connected to the ocean. It is landlocked and this causes the water to evaporate. This has led to a steady increase in its degree of salinity. Now the salinity is so high such that the marine life cannot survive in it. This is why it is called the Dead Sea.
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Question 48 of 90
48. Question
- Which of these is not a quality of non-potable water?
Correct
Explanation
Saline water contains salt commonly known as sodium chloride (NaCl). Such water is called saline water. It is not suitable for drinking and is said to be non-potable water.
Incorrect
Explanation
Saline water contains salt commonly known as sodium chloride (NaCl). Such water is called saline water. It is not suitable for drinking and is said to be non-potable water.
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Question 49 of 90
49. Question
- Assertion (A): Water suitable for drinking is called as potable water.
Reasoning (R): Every one liter of potable water contains dissolved salts.
Correct
Explanation
The water suitable for drinking is called potable water. Every liter of potable water contains 1- 2 grams of dissolved salts, mainly common salt.
Incorrect
Explanation
The water suitable for drinking is called potable water. Every liter of potable water contains 1- 2 grams of dissolved salts, mainly common salt.
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Question 50 of 90
50. Question
- State some of the minerals found in potable water?
Correct
Explanation
In addition to the common salt, there are small amounts of calcium (Ca), magnesium (Mg), potassium (K), copper (Cu) and zinc (Zn). The minerals in water give it a certain taste. In addition, these minerals are useful for our body’s metabolism. Potable water also contains dissolved air.
Incorrect
Explanation
In addition to the common salt, there are small amounts of calcium (Ca), magnesium (Mg), potassium (K), copper (Cu) and zinc (Zn). The minerals in water give it a certain taste. In addition, these minerals are useful for our body’s metabolism. Potable water also contains dissolved air.
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Question 51 of 90
51. Question
- What are the characteristics of the potable water?
Correct
Explanation
The following are the characteristics of potable water.
- Potable water should be colorless and odorless.
- It should be transparent.
- It should be free from harmful micro-organisms such as bacteria, virus and protozoa.
- It should be free from suspended impurities.
- It should contain some minerals and salts, necessary for our body and some dissolved gases to add taste.
Incorrect
Explanation
The following are the characteristics of potable water.
- Potable water should be colorless and odorless.
- It should be transparent.
- It should be free from harmful micro-organisms such as bacteria, virus and protozoa.
- It should be free from suspended impurities.
- It should contain some minerals and salts, necessary for our body and some dissolved gases to add taste.
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Question 52 of 90
52. Question
- What is the approximate percentage of fresh water available in rivers and lakes?
Correct
Explanation
Out of the total fresh water available on the earth only 1% is present in water bodies such as rivers and lakes and the rest is frozen in glaciers and polar-regions.
Incorrect
Explanation
Out of the total fresh water available on the earth only 1% is present in water bodies such as rivers and lakes and the rest is frozen in glaciers and polar-regions.
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Question 53 of 90
53. Question
- Which of these is not a water borne disease?
Correct
Explanation
Water from these water bodies is unfit for drinking, cooking, washing or bathing because it contains suspended and dissolved impurities. It also contains micro-organisms such as bacteria. If this water is consumed without purifying, it can cause water-borne diseases such as typhoid and cholera. Therefore, before water reaches our homes, it is treated and purified to make it potable. In conventional water treatment plants water is subjected to different processes for purification.
Incorrect
Explanation
Water from these water bodies is unfit for drinking, cooking, washing or bathing because it contains suspended and dissolved impurities. It also contains micro-organisms such as bacteria. If this water is consumed without purifying, it can cause water-borne diseases such as typhoid and cholera. Therefore, before water reaches our homes, it is treated and purified to make it potable. In conventional water treatment plants water is subjected to different processes for purification.
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Question 54 of 90
54. Question
- Which of these are added in the process of loading to speed up the sedimentation?
Correct
Explanation
Water from lakes or rivers is collected in large sedimentation tanks. There, it is allowed to stand undisturbed so that suspended impurities settle down at the bottom of the tank. Sometimes, a chemical substance such as potash alum is added to water, to speed up the process of sedimentation. This process is called loading. The particles of potash alum combine with the suspended impurities and make them settle down at a faster rate.
Incorrect
Explanation
Water from lakes or rivers is collected in large sedimentation tanks. There, it is allowed to stand undisturbed so that suspended impurities settle down at the bottom of the tank. Sometimes, a chemical substance such as potash alum is added to water, to speed up the process of sedimentation. This process is called loading. The particles of potash alum combine with the suspended impurities and make them settle down at a faster rate.
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Question 55 of 90
55. Question
- Which of these layers are present in a water filtration tank?
Correct
Explanation
Water from the sedimentation tanks is then pumped to the filtration tanks. Filtration tanks contain filter beds made up of gravel, sand, pebbles, activated charcoal and concrete. Water passes through these layers and becomes free from any remaining dissolved or suspended impurities completely.
Incorrect
Explanation
Water from the sedimentation tanks is then pumped to the filtration tanks. Filtration tanks contain filter beds made up of gravel, sand, pebbles, activated charcoal and concrete. Water passes through these layers and becomes free from any remaining dissolved or suspended impurities completely.
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Question 56 of 90
56. Question
- Choose the correct statements.
- i) Filtered water is treated chemically to remove the bacteria and the germs.
- ii) Chlorine and ozone are the chemicals used in the sterilization process.
iii) Chlorination is the process of adding adequate amount of chlorine to remove bacteria and germs.
Correct
Explanation
The filtered water is treated chemically to remove the remaining germs or bacteria. This process is called sterilization. The chemicals that are used in this process are chlorine and ozone. The process of adding chlorine in adequate amounts to water is called chlorination. The water from filtration tanks is pumped into chlorination tanks, where chlorine is added to remove harmful bacteria and other germs.
Incorrect
Explanation
The filtered water is treated chemically to remove the remaining germs or bacteria. This process is called sterilization. The chemicals that are used in this process are chlorine and ozone. The process of adding chlorine in adequate amounts to water is called chlorination. The water from filtration tanks is pumped into chlorination tanks, where chlorine is added to remove harmful bacteria and other germs.
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Question 57 of 90
57. Question
- Which is used to kill the germs in water in the Ozonization process?
Correct
Explanation
Ozonization is a process in which water is treated with ozone gas to kill the germs present in it.
Incorrect
Explanation
Ozonization is a process in which water is treated with ozone gas to kill the germs present in it.
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Question 58 of 90
58. Question
- Assertion (A): Sterilization is done by exposing water to air and sunlight.
Reasoning (R): Oxygen from air and sunlight destroy the germs in the water.
Correct
Explanation
The sterilization of water can also be done by exposing it to air and sunlight. Oxygen from the air and sunlight destroy the germs present in water.
Incorrect
Explanation
The sterilization of water can also be done by exposing it to air and sunlight. Oxygen from the air and sunlight destroy the germs present in water.
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Question 59 of 90
59. Question
- Which of the process uses air under pressure to kill germs in the water?
Correct
Explanation
Aeration is the process in which air under pressure is blown into filtered water. This also helps to kill the germs.
Incorrect
Explanation
Aeration is the process in which air under pressure is blown into filtered water. This also helps to kill the germs.
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Question 60 of 90
60. Question
- Which of these statements are not true about the RO purifiers?
Correct
Explanation
RO purifiers are the purifiers that can remove the dissolved impurities and germs. They also improve the taste of water. RO stands for the name of the technology, reverse osmosis, used in these purifiers. Some RO purifiers also have a UV (ultraviolet) unit that destroys the germs present in water.
Incorrect
Explanation
RO purifiers are the purifiers that can remove the dissolved impurities and germs. They also improve the taste of water. RO stands for the name of the technology, reverse osmosis, used in these purifiers. Some RO purifiers also have a UV (ultraviolet) unit that destroys the germs present in water.
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Question 61 of 90
61. Question
- In which of these water soaps and detergents forms lather easily?
Correct
Explanation
We use soaps and detergents to wash clothes. They form lather with water that quickens the process of removal of dirt from the clothes. Water contains a number of dissolved salts and minerals. When these salts are present in very small quantities in water it is called soft water. In this water, soaps or detergents form lather easily.
Incorrect
Explanation
We use soaps and detergents to wash clothes. They form lather with water that quickens the process of removal of dirt from the clothes. Water contains a number of dissolved salts and minerals. When these salts are present in very small quantities in water it is called soft water. In this water, soaps or detergents form lather easily.
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Question 62 of 90
62. Question
- Which of these makes difficult to remove the dirt from the hard water?
Correct
Explanation
Sometimes, minerals and salts are present in water in such a large quantity that soaps or detergents form a thick precipitate called scum instead of forming lather. This makes the removal of further dirt difficult. Such water is called hard water.
Incorrect
Explanation
Sometimes, minerals and salts are present in water in such a large quantity that soaps or detergents form a thick precipitate called scum instead of forming lather. This makes the removal of further dirt difficult. Such water is called hard water.
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Question 63 of 90
63. Question
- Assertion (A): The Hardness of water may be temporary or permanent.
Reasoning (R): The dissolved salts of calcium and magnesium are the reason for the hardness of water.
Correct
Explanation
Hardness of water is due to the presence of dissolved salts of calcium and magnesium. Hardness may be temporary or permanent.
Incorrect
Explanation
Hardness of water is due to the presence of dissolved salts of calcium and magnesium. Hardness may be temporary or permanent.
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Question 64 of 90
64. Question
- Choose the correct statements.
i) The permanent hardness of the water is due to the chloride salts of calcium and magnesium.
ii) The presence of carbonate and bicarbonate salts of calcium and magnesium makes the water hard.
Correct
Explanation
Temporary hardness is due to the presence of carbonate and bicarbonate salts of calcium and magnesium and permanent hardness results due to the presence of chloride and sulphate salts of calcium and magnesium.
Incorrect
Explanation
Temporary hardness is due to the presence of carbonate and bicarbonate salts of calcium and magnesium and permanent hardness results due to the presence of chloride and sulphate salts of calcium and magnesium.
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Question 65 of 90
65. Question
- What are the disadvantages of the hard water?
Correct
Explanation
Disadvantages of Hard water
- It is not good for washing clothes. It forms scum with soap and detergents, which makes the soap ineffective and also spoils the clothes further.
- It damages the utensils and containers in which it is stored and forms a hard layer.
- It forms scales on the machine parts used in industries and decreases their efficiency.
- It results in stomach ailments if consumed for a long period.
Incorrect
Explanation
Disadvantages of Hard water
- It is not good for washing clothes. It forms scum with soap and detergents, which makes the soap ineffective and also spoils the clothes further.
- It damages the utensils and containers in which it is stored and forms a hard layer.
- It forms scales on the machine parts used in industries and decreases their efficiency.
- It results in stomach ailments if consumed for a long period.
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Question 66 of 90
66. Question
- Which of these can be easily removed by boiling the water?
Correct
Explanation
Boiling: Temporary hardness is easily removed from water by boiling. When heated, the calcium hydrogen carbonate decomposes producing insoluble calcium carbonate. The insoluble carbonates are then filtered and removed from water. This makes the hard water soft and fit for use.
Incorrect
Explanation
Boiling: Temporary hardness is easily removed from water by boiling. When heated, the calcium hydrogen carbonate decomposes producing insoluble calcium carbonate. The insoluble carbonates are then filtered and removed from water. This makes the hard water soft and fit for use.
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Question 67 of 90
67. Question
- Choose the correct statements.
i) Washing soda is used to remove temporary and permanent hardness of water.
ii) Washing soda converts the chlorides and sulphates into insoluble carbonates.
iii) The insoluble carbonates are removed by distillation method.
Correct
Explanation
Adding washing soda: Washing soda is used to remove permanent hardness of water. Adding washing soda converts chlorides and sulphates into insoluble carbonates. These insoluble carbonates are removed by filtration.
Incorrect
Explanation
Adding washing soda: Washing soda is used to remove permanent hardness of water. Adding washing soda converts chlorides and sulphates into insoluble carbonates. These insoluble carbonates are removed by filtration.
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Question 68 of 90
68. Question
- Assertion (A): Ion-exchange method converts hard water into soft water.
Reasoning (R): The calcium and magnesium ions are replaced by sodium ions in ion-exchange method.
Correct
Explanation
Ion – exchange: Another method used to remove the hardness of water is to pass it through a column of ion-exchange resins where calcium and magnesium ions get replaced by sodium ions. This converts hard water into soft water.
Incorrect
Explanation
Ion – exchange: Another method used to remove the hardness of water is to pass it through a column of ion-exchange resins where calcium and magnesium ions get replaced by sodium ions. This converts hard water into soft water.
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Question 69 of 90
69. Question
- Choose the Incorrect statements.
i) Water obtained after distillation is called as distilled water.
ii) Distillation process removes the permanent hardness of the water.
iii) Distilled water is the purest form of water.
Correct
Explanation
Temporary and permanent hardness both can be removed by the method of distillation. The water obtained after distillation is called distilled water. It is the purest form of water.
Incorrect
Explanation
Temporary and permanent hardness both can be removed by the method of distillation. The water obtained after distillation is called distilled water. It is the purest form of water.
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Question 70 of 90
70. Question
- Which of these is not the reason for taste of the water?
Correct
Explanation
Distilled water and boiled water have no taste. The pleasant taste of drinking water is due to the presence of dissolved substances which include air, carbon dioxide and minerals.
Incorrect
Explanation
Distilled water and boiled water have no taste. The pleasant taste of drinking water is due to the presence of dissolved substances which include air, carbon dioxide and minerals.
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Question 71 of 90
71. Question
- Choose the incorrect statements.
i) Fresh water sources are useful for domestic, agricultural and industrial usage.
ii) Surface water is the only source of fresh water.
iii) Rivers, reservoirs and tanks are the examples of fresh water sources.
Correct
Explanation
Fresh water resources are the sources of water that are useful to society for domestic, agricultural or industrial uses. These include surface and ground water. Examples of surface water include rivers, reservoirs, Eris and tanks.
Incorrect
Explanation
Fresh water resources are the sources of water that are useful to society for domestic, agricultural or industrial uses. These include surface and ground water. Examples of surface water include rivers, reservoirs, Eris and tanks.
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Question 72 of 90
72. Question
- How many major river basins are there in Tamil Nadu?
Correct
Explanation
There are 17 major river basins in Tamil Nadu with 61 reservoirs and approximately 41,948 tanks. Eris and tanks are traditionally used in Tamil Nadu to collect rainfall during the monsoon which can be used throughout the year.
Incorrect
Explanation
There are 17 major river basins in Tamil Nadu with 61 reservoirs and approximately 41,948 tanks. Eris and tanks are traditionally used in Tamil Nadu to collect rainfall during the monsoon which can be used throughout the year.
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Question 73 of 90
73. Question
- Which of these are called as aquifers?
Correct
Explanation
Groundwater sources are called aquifers. Aquifers are layers below the ground made of coarse and gravel that contain spaces allowing rainwater collection. The use of groundwater is possible through open wells and bore wells.
Incorrect
Explanation
Groundwater sources are called aquifers. Aquifers are layers below the ground made of coarse and gravel that contain spaces allowing rainwater collection. The use of groundwater is possible through open wells and bore wells.
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Question 74 of 90
74. Question
- Which of these substances pollute the water bodies?
Correct
Explanation
Shampoo, face wash, shower gel and toothpaste have small round pieces of plastic added to them. These are called micro beads. They are added for different reasons like scrub and clean your skin, polish your teeth etc. When we use products with micro beads, they go down our drain and pollute water bodies. Fish and other animals eat them by accident and get sick.
Incorrect
Explanation
Shampoo, face wash, shower gel and toothpaste have small round pieces of plastic added to them. These are called micro beads. They are added for different reasons like scrub and clean your skin, polish your teeth etc. When we use products with micro beads, they go down our drain and pollute water bodies. Fish and other animals eat them by accident and get sick.
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Question 75 of 90
75. Question
- What is called as Eutrophication?
Correct
Explanation
Fertilizers, pesticides and insecticides used in agriculture can dissolve in rainwater and flow into water bodies such as rivers and lakes. This causes an excess of nutrients such as nitrates and phosphates as well as toxic chemicals in water bodies which is called Eutrophication and they can also be harmful to aquatic life.
Incorrect
Explanation
Fertilizers, pesticides and insecticides used in agriculture can dissolve in rainwater and flow into water bodies such as rivers and lakes. This causes an excess of nutrients such as nitrates and phosphates as well as toxic chemicals in water bodies which is called Eutrophication and they can also be harmful to aquatic life.
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Question 76 of 90
76. Question
- Which of these substances are released as toxic waste by Industries?
Correct
Explanation
Many industries release toxic waste such as lead, mercury, cyanides, cadmium, etc. If this waste is unregulated and is released into water bodies it negatively impacts humans, plants, animals and aquatic life.
Incorrect
Explanation
Many industries release toxic waste such as lead, mercury, cyanides, cadmium, etc. If this waste is unregulated and is released into water bodies it negatively impacts humans, plants, animals and aquatic life.
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Question 77 of 90
77. Question
- Which of these is not a domestic pollutant?
Correct
Incorrect
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Question 78 of 90
78. Question
- Which of these are pollutants from the domestic detergents?
Correct
Explanation
Incorrect
Explanation

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Question 79 of 90
79. Question
- What are the negative effects of the DDT used for agricultural purpose?
Correct
Incorrect
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Question 80 of 90
80. Question
- Assertion (A): Fertilizers used for agricultural purposes decrease the animal and plant diversity.
Reasoning (R): Bacteria’s and algae uses these fertilizers to grow faster and use all the dissolved oxygen in water.
Correct
Explanation
Incorrect
Explanation

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Question 81 of 90
81. Question
- Which of these are the major pollutants from the industrial sectors?
Correct
Incorrect
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Question 82 of 90
82. Question
- What are the effects of the Industrial pollutants?
Correct
Incorrect
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Question 83 of 90
83. Question
- Which of these industries is the major cause for pollution?
Correct
Explanation
Incorrect
Explanation

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Question 84 of 90
84. Question
- What are the effects of oil spills on the water surface?
Correct
Explanation
Oil spills cause water pollution which is harmful to aquatic life. The oil which remains floating on the water surface blocks sunshine, reduces the oxygen dissolved in water and suffocates marine organisms.
Incorrect
Explanation
Oil spills cause water pollution which is harmful to aquatic life. The oil which remains floating on the water surface blocks sunshine, reduces the oxygen dissolved in water and suffocates marine organisms.
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Question 85 of 90
85. Question
- Choose the Incorrect statements.
i) Thermal and Nuclear power plants use a large amount of water for cooling purposes.
ii) The water from nuclear and thermal plants is discharged back to the water source at a very low temperature.
iii) The chemicals and the temperature rise in the discharges water decrease the dissolved oxygen in the water.
Correct
Explanation
Large amounts of water are used for cooling purposes in thermal and nuclear power plants and many industries. Water used for cooling purposes is discharged back to a river or to original water source at a raised temperature and sometimes with chemicals. This rise in temperature decreases the amount of oxygen dissolved in water which adversely affects the aquatic life.
Incorrect
Explanation
Large amounts of water are used for cooling purposes in thermal and nuclear power plants and many industries. Water used for cooling purposes is discharged back to a river or to original water source at a raised temperature and sometimes with chemicals. This rise in temperature decreases the amount of oxygen dissolved in water which adversely affects the aquatic life.
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Question 86 of 90
86. Question
- Which is not a major category of pollutants?
Correct
Explanation
Pollutants are generally classified as domestic pollutants, agricultural pollutants and industrial pollutants.
Incorrect
Explanation
Pollutants are generally classified as domestic pollutants, agricultural pollutants and industrial pollutants.
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Question 87 of 90
87. Question
- Choose the correct statements.
i) Micro-plastics are found only in bottled water and tap waters around the world.
ii) Micro-plastics can be found in almost every saline water source.
Correct
Explanation
Micro-plastics can be found in almost every freshwater source. They have been found from the freezing waters of the Arctic and Antarctic to the bottom of the deep-sea floor up to 5,000 meters deep. Micro plastics have been found in bottled water and tap water around the world.
Incorrect
Explanation
Micro-plastics can be found in almost every freshwater source. They have been found from the freezing waters of the Arctic and Antarctic to the bottom of the deep-sea floor up to 5,000 meters deep. Micro plastics have been found in bottled water and tap water around the world.
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Question 88 of 90
88. Question
- What is the major source of water pollution in India?
Correct
Explanation
The largest source of water pollution in India is untreated sewage. On an average, a person uses 180 liters of water per day for washing clothes, cooking, bathing, etc.
Incorrect
Explanation
The largest source of water pollution in India is untreated sewage. On an average, a person uses 180 liters of water per day for washing clothes, cooking, bathing, etc.
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Question 89 of 90
89. Question
- What are the methods used for reducing water pollution?
Correct
Explanation
Some simple ideas to avoid water pollution are given below:
- Use detergents that are biodegradable and avoid those that contain toxic chemicals.
- Wear clothing that is made from natural fibres such as cotton and avoid wearing synthetic fibres such as nylon.
- Domestic waste water should be treated properly, and all harmful substances should be removed from it, so it can be reused for flushing toilets and gardening.
- Use bio-pesticides (natural pest control) instead of chemical pest control.
- Use compost made from cow dung, garden waste and kitchen waste as a fertilizer.
- Water released from industries should be treated before being discharged.
Incorrect
Explanation
Some simple ideas to avoid water pollution are given below:
- Use detergents that are biodegradable and avoid those that contain toxic chemicals.
- Wear clothing that is made from natural fibres such as cotton and avoid wearing synthetic fibres such as nylon.
- Domestic waste water should be treated properly, and all harmful substances should be removed from it, so it can be reused for flushing toilets and gardening.
- Use bio-pesticides (natural pest control) instead of chemical pest control.
- Use compost made from cow dung, garden waste and kitchen waste as a fertilizer.
- Water released from industries should be treated before being discharged.
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Question 90 of 90
90. Question
- Which of these is not a category of wastes?
Correct
Explanation
Do not throw waste such as plastics into water bodies. Always separate your waste into recyclable, non-recyclable and biodegradable so that it does not cause pollution.
Incorrect
Explanation
Do not throw waste such as plastics into water bodies. Always separate your waste into recyclable, non-recyclable and biodegradable so that it does not cause pollution.
Leaderboard: Water Online Test 8th Science Lesson 18 Questions in English
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