Give reasons for the following:

The presence of ozone layer is a boon to human being.

Give reasons for the following:

Ionosphere is important in long distance radio-wave communication.

The proportion of Nitrogen in the atmosphere is about

1. 80%
2. 21%
3. 78%
4. 65%

Which of the following is the lower most layer of the atmosphere?

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