Which amongst the following is not a domain of the Biosphere?

1. Lithosphere
2. Exosphere
3. Hydrosphere
4. Atmosphere

………….. extends up to a height of about 400 km and is responsible for enabling radio communication.

1. Mesosphere
2. Ionosphere
3. Stratosphere
4. Troposphere

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.

Name the uppermost layer in the structure of the atmosphere that gradually merges with interplanetary space.

1. Ionosphere
2. Exosphere
3. Troposphere
4. Mesosphere