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Page No 196:

Question 1:

Potable water is to be used for
(a) washing cars.
(b) drinking and cooking.
(c) washing clothes.
(d) toilets.

Answer:

(b) drinking and cooking
Potable water is clean; therefore, it is fit for drinking and cooking.

Page No 196:

Question 2:

Too much rainfall can cause
A. drought.
B. floods.
C. water-borne diseases.
D. destruction of houses.

(a) A and B are correct.
(b) B and C are correct.
(c) B, C and D are correct.
(d) A and D are correct.

Answer:

(c) B, C and D are correct.
Excessive rain causes floods and can destruct houses. Meanwhile, stagnant water provides breeding place for mosquitoes and also spreads water-borne diseases.

Page No 196:

Question 3:

Which of these represents the water cycle correctly?
(a) water on land and sea → evaporation → water vapour → clouds → rain
(b) water on land and sea → condensation → clouds → rain → ground water
(c) water on land and sea → evaporation → rain → clouds

Answer:

(a) water on land and sea → evaporation → water vapour → clouds → rain

The water from water bodies gets evaporated due to heat and forms water vapours in the air. Water vapours form clouds. When clouds cannot hold more water, it comes down as rain.

Page No 196:

Question 4:

In an earlier chapter, you have learnt about a process by which pure water can be obtained from salt water. Which is that process?
(a) distillation
(b) sedimentation
(c) decantation
(d) filtration

Answer:

(a) distillation
Distillation separates salt from water and gives pure water.



Page No 197:

Question 5:

Why do you think this process is not widely used to get pure water?
(a) It needs a lot of energy to heat the salt water.
(b) It is very costly.
(c) Enormous quantities of water would have to be purified to supply entire cities.
(d) All the above.

Answer:

(d) All the above
Distillation is an expensive process and it requires large amount of heat energy. Also, cities need immense water; therefore, large amount of water needs to be purified.

Page No 197:

Question 6:

In the table given below, what can replace X?

Group I Group II Group III
sedimentation river transpiration
coagulation sea evaporation
X wells condensation
chlorination bore well precipitation
(a) surface run-off
(b) filtration
(c) rain
(d) ponds

Answer:

(b) filtration
Group I represents methods of separation and filtration is one of them.

Page No 197:

Question 7:

Which of the following statements is true?
(a) Water which looks clean and sparkling is fit to drink.
(b) Rainwater is the purest form of water.
(c) The process by which plants release water is called surface run-off.
(d) The coming down of water in the form of rain, hail and snow is called perspiration.

Answer:

(b) Rain water is the purest form of water

Page No 197:

Question 8:

Match the items in column I to those in column II.

Column I Column II
i. distillation A. lead
ii. pollutant B. saline
iii. potable C. pure water
iv. seawater D. drinkable

Which set of answers is correct?
(a) i-A; ii-C; iii-B; iv-D
(b) i-A; ii-C; iii-D; iv-B
(c) i-C; ii-A; iii-B; iv-D
(d) i-C; ii-A; iii-D; iv-B

Answer:

(d) i-C; ii-A; iii-D; iv-B
Distillation gives pure water. Lead is a pollutant. Potable water is fit for drinking and seawater is saline.

Page No 197:

Question 9:

The rainfall for a week in June in Kerala was recorded in a graph. Flooding occurs if the total rainfall over a three-day period exceeds 40 mm. Study the graph and find out the number of times flooding would have occurred in the locality during the entire week?
Figure

(a) never
(b) once
(c) twice
(d) thrice

Answer:

(b) once
Flood occurred after rainfall on Wednesday.

Page No 197:

Question 10:

Explain the following terms: aquifers, drought, rainwater harvesting, water pollution, deforestation.

Answer:

Aquifers: Reservoirs of underground water are called aquifers.
Drought: Scarcity of rain over a long period of time is called draught.
Rainwater: It is the water that flows down from the clouds.
Harvesting: It is the process of collecting and storing water.
Water pollution: It is an act of contaminating water that makes it unfit for drinking.
Deforestation: It is an act of cutting down of trees on massive scale.

Page No 197:

Question 11:

What is the state of water at X and Y?
Figure

(a) X-vapour, Y-solid
(b) X-vapour; Y-liquid
(c) X-liquid; Y-vapour
(d) X-solid; Y-vapour

Answer:

(c) X-liquid; Y-vapour
X shows loss of water due to transpiration and Y shows water loss due to evaporation.



Page No 198:

Question 12:

Are the following statements true or false?
(a) Deforestation is one method of conservation.
(b) Drought conditions affect all life forms.
(c) Floods only affect human beings.
(d) In some countries, seawater is purified to make it fit for human consumption.
(e) Sewage should be treated for the removal of harmful wastes before it is released into the river.

Answer:

(a) Deforestation is one method of conservation.
False. Afforestation is one method of conservation.

(b) Drought conditions affect all life forms.
True

(c) Floods only affect human beings.
False. Floods affect all life forms of the affected area.

(d) In some countries, seawater is purified to make it fit for human consumption.
True

(e) Sewage should be treated for the removal of harmful wastes before it is released into the river.
True

Page No 198:

Question 13:

What is rainwater harvesting? Explain in a few sentences how it can be carried out in houses. What can this water be used for?

Answer:

Rainwater harvesting refers to accumulation and deposition of rainwater for reuse.
Rainwater harvesting can be done in houses by collecting the rainwater. When rainwater falls on roofs, it is allowed to pass through pipes. Further, this water is collected and stored in a tank at ground level or in a boring well.
This water can be used directly in gardens or for cleaning. However, this water is not fit for drinking.

Page No 198:

Question 14:

(a) You are given a glass full of muddy water. The steps you should take to get clear water from it are listed below. Arrange these steps in the correct order.
(i) Line a funnel with filter paper or cloth.
(ii) Allow the water to stand, without disturbing it.
(iii) Gently pour out the liquid portion into another glass.
(iv) Throw away the thick muddy water left behind in the first glass.
(v) Pour the water into the funnel.
(vi) The mud particles, being heavier, will settle at the bottom.
(vii) Collect the clear water that comes through the funnel.
(b) Give a single word that explain the steps described in ii and v.
(c) What else can you do to help remove the mud particles from the water? What is this process called?
(d) Do you think this water is now safe to drink? Why?
(e) Name one simple way be which this water can be made safe for drinking.

Answer:

(a) The correct order is as follows:
(ii) Allow the water to stand, without disturbing it.
(vi) The mud particles, being heavier, will settle at the bottom.
(iii) Gently pour out the liquid portion into another glass.
(iv) Throw away the thick muddy water left behind in the first glass.
(i) Line a funnel with filter paper or cloth.
(v) Pour the water into the funnel.
(vii) Collect the clear water that comes through the funnel.

(b) Steps (ii) and (v) are sedimentation and filtration, respectively.

(c) The mud particles can be settled and removed by adding alum. This process is called loading.

(d) This water is not fit for drinking as it still has disease-causing bacteria and germs.

(e) By boiling, this water can be made fit for drinking. Boiling of water will kill all the germs.

Page No 198:

Question 15:

Explain, with examples, why water is essential for all living things.

Answer:

Water is essential for all living things. Water is called wonder liquid as it can dissolve many substances. This property enables water to be a solvent. Most of the chemical reactions of the living world is carried out in water as a medium. The body of all living things needs water as a medium for all metabolic reactions.
Further, water is needed for drinking. We also need water for cooking, washing and bathing.

Page No 198:

Question 16:

Is water a renewable or a non-renewable resource? Justify your answer.

Answer:

Water is a renewable source, as it can be replenished again and again by water cycle. Moreover, it does not take millions of years to replenish water.

Page No 198:

Question 17:

In what ways can factories cause pollution of the water supply? Name three metals whose compounds can cause serious illness.

Answer:

Factories discharge their untreated wastes in water bodies. This causes pollution of water supply. Such waste contains poisonous metals that are harmful for health. They also kill plants and animals in water. The metal compounds that can cause serious illness are lead, cadmium and mercury compounds.

Page No 198:

Question 18:

Name the following:
(a) a solid that dissolves in water
(b) a solid that is insoluble in water
(c) a liquid that is miscible in water
(d) a liquid that is immiscible in water
(e) a solution in water where the solute is a gas

Answer:

(a) Salt is a solid that dissolves in water.
(b) Sand is a solid that is insoluble in water.
(c) Milk is a liquid that is miscible in water.
(d) Cooking oil is a liquid that is immiscible in water.
(e) Cold drink is a solution in water where the solute is a gas.

Page No 198:

Question 19:

Replace the following with a word or a phrase.
(a) resources that go through cycles and can be replenished
(b) water that is fit to drink
(c) that process of removing salt from water
(d) the coming down of water in the form of rain, hail and snow
(e) reservoirs of underground water
(f) indiscriminate cutting down of trees
(g) condition caused by absence of rain over a long period of time
(h) water infected with undesirable germs and wastes
(i) condition caused by excess rain in a region

Answer:

(a) Renewable sources are the resources that go through cycles and can be replenished.
(b) Potable water is the water that is fit to drink.
(c) Distillation is the process of removing salt from water.
(d) Precipitation is the coming down of water in the form of rain, hail and snow.
(e) Aquifers are the reservoirs of underground water.
(f) Deforestation is the indiscriminate cutting down of trees.
(g) Drought is a condition caused by absence of rain over a long period of time.
(h) Contaminated water is the water infected with  germs and waste.
(i) Flood is caused by excess rain in a region.



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