# Hot Questions : Thinks and answer : (Lesson : 16)1) Can you think of one observation in your daily life which shows the presence of water vapour in the air?2) Is it good to sleep under a tree a) during the day, b) at night? Give reasons.3) People living in a certain region have a high incidence of skin cancer. Can you identify one possible cause for this?4) Why do you think air becomes thinner higher up?(Hint: think of which force holds the atmosphere to the earth)5) An aquarium owner, on a rather cold day. Put a heater in his aquarium, which made the water warm, but not hot. He thought the fish would like that. However, all his fish died. What could be the reason for this?

1)  Can you think of one observation in your daily life which shows the presence of water vapour in the air?
If you put a piece of ice inside a glass you will see water droplets outside the glass. This is because the water vapour present in air condensed when come in touch of the cooler glass.

2)  Is it good to sleep under a tree a) during the day, b) at night? Give reasons.
At night tree emits CO2 by respiration. But at day time it emits O2 by photosynthesis. Thus it is good to sleep under tree at day time.

3) People living in a certain region have a high incidence of skin cancer. Can you identify one possible cause for this?
In some region ozone layer depletion is higher. For this reason UV ray comes directly and falls on the skin, which can cause cancer.

4)  Why do you think air becomes thinner higher up? (Hint: think of which force holds the atmosphere to the earth)
Density of gas molecules is higher at ground level because the pressure of the gas weight on them. Thus at higher level gas pressure decreases.
As we move upward the gravitational attraction forces decreases. Thus the weights of the gas molecules are lesser at high altitude. This also decrease the gas pressure at higher altitude.

5)  An aquarium owner, on a rather cold day. Put a heater in his aquarium, which made the water warm, but not hot. He thought the fish would like that. However, all his fish died. What could be the reason for this?
As he heat water, dissolve oxygen goes out. Aquatic animals (fish) respirate by taking the dissolved oxygen. As oxygen goes off, fish dies.

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