Q.1. Non-renewable resources

Ans: (b) can be replaced but the time of replacement varies from a few hundred to millions of years.

Non-renewable resources, once used up, take millions of years to form.

Q.2. Which of these methods does not result in conservation of water?

Ans: (c) cutting vegetation so that less water is lost by transpiration

Trees slow down the flow of rainwater on land and increase the absorption by soil. Therefore, if vegetation is cut, the absorption of rainwater by the soil will decrease.

Q.3. Renewable resources need to be conserved because

Ans: (a) we should not use them faster than they are replenished by nature.

Renewable resources are exhaustible and we need to conserve them. We should not use them faster than they are replenished by nature.

Q.4. How much of the earth's surface is covered with water?

Ans: (b) about three-fourths

Nearly three-fourth of the earth's surface is covered with water.

Q.5. As a natural resource, groundwater is

Ans: (a) renewable and exhaustible

Groundwater is a renewable and exhaustible natural resource.

Q.6. The water table in an area will go down when

Ans: (c) we use groundwater faster than it is replenished

If we use groundwater in an area faster than it is replenished, water table will go down.

Q.7. The boiling and melting points of water are

Ans: (a) 100°C and 0°C

Water starts boiling at 100°C to form steam. Ice melts at 0°C to form water.

Q.8. The water table goes down due to

Ans: (d) all of these

All these factors −- population growth, increased agriculture and increased industrialisation −- are responsible for the lowering of the water table.

Q.9. Using less water and preventing water from getting polluted is called ___________ of water.

Ans: Using less water and preventing water from getting polluted is called conservation of water.

Q.10. Buildings and roads reduce __________ of water by the soil.

Ans: Buildings and roads reduce seepage of water by the soil.

Q.11. Rainwater harvesting lowers the water table. True / false?

Ans: Given statement is false. Rainwater harvesting raises the water table. Under this process, rainwater is allowed to fall on roofs of the buildings to flow into a deep trench in the ground. This rainwater replenishes the water table instead of flowing down to the drains.

Q.12. All renewable resources are inexhaustible. True / false?

Ans: Given statement is false. All renewable resources are not inexhaustible and some of them like soil, forest, and groundwater are exhaustible.

Q.13. Groundwater is a non-renewable resource. True / false?

Ans: False; groundwater is a renewable resource because it can be renewed by rainwater.

Q.14. Population growth is a major reason for water scarcity. True / false?

Ans: It is a true that population growth is a major reason for water scarcity. As population increases, more water is needed for drinking, cooking, washing, cleaning, construction work etc. Excess consumption of water for these purposes leads to water scarcity.

Q.15. Groundwater is generally free from suspended impurities. True / false?

Ans: Given statement is true. On passing through the soil, groundwater gets filtered by various layers of sand and rocks, which make it free from suspended impurities.

Q.16. Preventing pollution of a natural resource is a part of conservation. True / false?

Ans: Given statement is true. If we prevent a natural resource from getting polluted, we in turn increase the amount of that clean natural resource. This leads to its conservation for future.

Q.17. Is water on the earth a renewable or a non-renewable resource?

Ans: Water is a renewable resource and is inexhaustible because it can constantly be recycled by water cycle. 

Q.18. Out of every 1 litre of water on the earth, only 10 mL is available to us as freshwater on the surface of the earth. In what forms is the rest of the water available?

Ans: Out of the total proportion of water present on the Earth, about 97.4% is constituted by the ocean and sea water. Approximately 2% of the total water is present in the form of polar icecaps. The remaining portion of water is present in the form of fresh water. 

Q.19. The molecules of water, ice and steam are the same. Do you agree?

Ans: Yes, steam, ice and water are formed of the same molecules. These three substances represent three physical states of water, but the basic composition of all these substances is same. 

Q.20. Water evaporates only when it is heated to 100°C. Do you agree? Give reasons.

Ans: No, water does not evaporate only when it is heated to 100°C. Evaporation is a surface phenomenon and occurs at almost all temperatures. However, an increase in the temperature increases the rate of evaporation. Thus, at 100°C only the rate of evaporation is increased. 

Q.21. A well was dug in a village up to the deepest level at which water was available. What is the level of groundwater in the village—the depth of the water surface in the well from the surface of the earth, or the depth from the surface of water in the well to the bottom of the well?

Ans: The level of groundwater in the village is the depth from the surface of the water in the well to the bottom of the well. 

Q.22. Deforestation is a reason for depletion of the water table. Do you agree? Give reasons.

Ans: Yes, deforestation is a major reason for the depletion of water table. The presence of vegetation and forest cover is essential for slowing down the rain water flow. This leads to progressive absorption of rainwater by the soil, which is essential for the maintenance of groundwater level. Due to deforestation, the rainwater is not effectively absorbed by the soil, which results in a decrease in water table. 

Q.23. What is the term used for 'the wise and careful use' of resources?

Ans: The term used to describe 'the wise and careful use' of resources is conservation. 

Q.24. Which method, according to you, is the most promising in raising the water table in a city?

Ans: The most appropriate method to raise the water table in a city is rainwater harvesting method. 

Q.25. Are natural resources living, non-living or both?

Ans: Natural resources are both living and non-living. Plants and animals are living natural resources, whereas air, soil, water, and minerals are non-living natural resources.

Q.26. What is the name given to the level at which groundwater is found?

Ans: The level at which groundwater is found is called water table.

Q.27. Why is there a shortage of water even through almost three-fourths of the earth is covered with water?

Ans: There is a shortage of water even though almost three-fourths of the earth is covered with water because 97.5% of water is sea and ocean water. This water cannot be used directly as it has high salt content.

Q.28. What are the three states of water? How can water be changed from one state to the other?

Ans: The three states of water are ice, water and steam. When ice is heated, it melts to form water. When water is boiled, it changes to steam.

Q.29. What happens to rainwater once it falls on the earth?

Ans: When rainwater falls on the earth, some of the water seeps through the soil and replenishes the groundwater.

Q.30. What do you mean by water table?

Ans: The spaces between the soil particles and the gaps between the rocks are filled with groundwater. The level of this groundwater is known as water table.

Q.31. How are natural springs of water formed?

Ans: Groundwater flows through the surface of non-porous rocks. At some places, it comes out of the surface and forms natural springs.

Q.32. What is drip irrigation?

Ans: Drip irrigation is a method in which water is supplied to the roots of the plants in drops instead of filling the entire field with water.

Q.33. How does planting trees help groundwater conservation?

Ans: Plants slow down the flow of rainwater on land and facilitates its absorption by soil. Hence, if we plant more trees, soil will absorb more rainwater and groundwater will be conserved.

Q.34. If a resource is renewable, it can still get exhausted. Discuss giving two examples.

Ans: Yes, if a resource is renewable, it can still get exhausted if we use it at a faster rate than it is renewed. It may also get exhausted if we disturb its natural method of renewal. For example, groundwater and trees are the renewable resources which can get exhausted if we use groundwater and cut trees at a faster rate for various purposes.

Q.35. Describe the water cycle in nature.

Ans: Water cycle:

Water present in water bodies including sea, oceans, rivers and lakes evaporates due to sun's heat. Water is further released in large amounts by the leaves of plants.

The water vapour rises up, cools down and condenses to form tiny droplets of water. These droplets unite to form clouds. This process keeps on repeating and water drops in the clouds fall on earth as rain. Sometimes, if temperature is very low, rainwater falls as hail or snow.

Q.36. Conservation of resources means avoiding their wasteful use. Does this definition cover all aspects of conservation? Explain.

Ans: Yes, conservation of resources means avoiding their wasteful use. However, this definition does not cover all aspects of conservation as reducing the pollution of natural resources such as air, water and soil is also a part of conservation. Besides, conservation also includes non-disturbance of natural processes by which resources are renewed.

Q.37. List four methods of conserving water.

Ans: Four methods of conserving water are:

Q.38. Explain one method of groundwater conservation whose importance has been realized recently.

Ans: One method of groundwater conservation whose importance has been realised recently is the rainwater harvesting. It is a method of storing rainwater for our future use. Rainwater, which falls on the roofs of houses, is allowed to flow into a deep trench in the ground. This process increases the level of groundwater. This process is successful and has given considerable results.

Q.39. If a resource can be replaced within ten years by natural processes, would you classify it as renewable of non-renewable? Give reasons.

Ans: If a resource can be replaced within ten years by natural processes, we would classify it as renewable because it is renewed within a reasonable time period.

Q.40. Why do we feel the need for conservation more today than our ancestors did?

Ans: We need to conserve more today than our ancestors did because of the following reasons:

Q.41. Wells dug to get groundwater often dry up after some time. Why? What can be done to the well to get water from it again?

Ans: Wells dug to get groundwater often dry after some time because of the decline in the water table. Wells should be dug deeper to get water from it again.

Q.42. Water vapour condenses to form drops of water higher up in the atmosphere. Why is the atmosphere cooler higher up?

Ans: The density of air decreases as we go higher up in the atmosphere. As the air becomes thinner, the temperature decreases. Moreover, the sun heats the surface of the earth due to which the lower atmosphere of the earth is also heated up. As we go up, the temperature decreases.

Hence, the atmosphere higher up is cooler as compared to the lower atmosphere.

Q.43. When the humidity is high and the temperature is low, fog often forms. Why?

Ans: When humidity is high and temperature is low, air cannot hold additional moisture and becomes supersaturated if additional moisture is added. This often leads to the formation of fog.

Q.44. You live near a river. You notice that your neighbours throw all their garbage into the river. They justify their action by saying that the garbage they throw is very little as compared to the dirt thrown into the river by the surrounding factories. Is this thinking correct? Explain.

Ans: No, this thinking is not correct. The contribution of each and every individual for saving and keeping our environment clean is very important. We should try to fulfil our duties towards the environment and lead others to follow them. 

They should stop throwing the garbage in the water body and find alternative ways to dispose it.

If they do so collectively, it can bring about a big change. Also, they can lead a campaign against these industries to stop putting their waste into the water body.

Q.45. Differentiate between renewable and non-renewable resources, giving two examples of each.

Ans: 

Q.46. What are the reasons for lowering of the water table in cities?

Ans: The reasons for lowering of the water table in cities are as follows:

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