Water

Samacheer Book Back Questions And Answers For Science Standard 8 “Water“

I. Choose the correct answer:
1. Water changes to ice at
a) 0ºC
b) 100ºC
c) 102ºC
d) 98ºC

2. Solubility of carbon dioxide in water is high when the
a) pressure is low
b) pressure is high
c) temperature is high
d) None of the above

3. The gas collected at the cathode on electrolysis of water is
a) oxygen
b) hydrogen
c) nitrogen
d) carbon dioxide

4. Which of the following is a water pollutant?
a) Lead
b) Alum
c) Oxygen
d) Chlorine

5. Permanent hardness of water is due to the presence of _____.
a) sulphates and chlorides
b) dust particles
c) carbonates and bicarbonates
d) other soluble particles

II. Fill in the blanks:
1. Water is colourless, odourless and _____.
2. The boiling point of water is _____.
3. Temporary hardness of water can be removed by _____ of water.
4. The density of water is maximum at _____.
5. Loading speeds up the process of _____.

Answers:
1. tasteless
2. 100°C
3. boiling
4. 4°C
5. dihydrogen monoxide H₂O

III. State true or false. If false, correct the statement:
1. Sewage should be treated well before being discharged it into water bodies.
2. Sea water is suitable for irrigation as it contains dissolved salts.
3. Excessive use of chemical fertilizers depletes the soil and causes water pollution.
4. The density of water will not change at all temperature
5. Soap lathers well in hard water.

Answers:
1. True
2. False (Sea water is not suitable for irrigation as it has high salinity)
3. True
4. False (The density of water is different at different temperatures)
5. False (Soap lathers well in soft water)

IV. Match the following:
1. Universal solvent      A. Water pollutant
2. Hard water                B. Kills germs
3. Boiling                       C. Ozonisation
4. Sterilization               D. Water
5. Sewage                      E. Stomach ailments

Answers:
1. D
2. E
3. B
4. C
5. A

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