31.
The gaseous envelope around the earth is known as atmosphere. The lowest layer of this is extended upto 10 km from sea level, this layer is

36.
Consider the following assertion and reason and select the correct answer:
Assertion (A) Ozone kills microorganism in water.
Reason (R) Ozone is not radioactive.

37.
Which one of the following group of gases contribute to the 'Green House Effect'?

39.
Which one of the following statements about temperature is correct?