The upper limit of the stratosphere is known as:

1. Stratopause
2. Statapause
3. Upper strata
4. Upper limital strata

Assertion (A): About 90 per cent of the mass of air lies within a height of about 20 km from the surface of the earth.

Reason (R): The air of the lower layer is always heavier or denser, while the upper layers are thinner or less dense.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.

Water vapour is added to the atmosphere by ……………. .

1. evaporation
2. transpiration
3. respiration
4. All of the above

Clouds and weather phenomenon occur in the Troposphere but some clouds are found in the Mesosphere. Why?

1. Meteoric dust particles reflect sunlight causing wispy clouds.
2. Some water particles reach the Mesosphere to form clouds.
3. Ions from the ionosphere deflect sunlight giving the impression of clouds.
4. None of the above.