# NCERT Class – 9 Science Solution: Chapter 1 Matter in Our Surroundings-Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 17

Classify the following into osmosis/diffusion

1. Swelling up of a raisin on keeping in water.
2. Spreading of virus on sneezing.
3. Earthworm dying on coming in contact with common salt.
4. Shrinking of grapes kept in thick sugar syrup.
5. Preserving pickles in salt.
6. Spreading of smell of cake being baked throughout the house.
7. Aquatic animals using oxygen dissolved in water during respiration.

1. Osmosis
2. Diffusion
3. Osmosis
4. Osmosis
5. Osmosis
6. Diffusion
7. Diffusion

Question 18

Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.

• In case of ice the water molecules have low energy while in the case of steam the water molecules have high energy.
• The high energy of water molecules in steam is transformed as heat and may cause burns.
• On the other hand, in case of ice, the water molecules take energy from the body and thus give a cooling effect.

Question 19

Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment.

The temperature of both boiling water and steam is but steam has more energy because of latent heat of vapourisation.

Question 20

A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator . If you could measure the temperature of the content of the tumbler, which of the following graphs (Figure) would correctly represent the change in its temperature as a function of time.