Question

Why air is better respiratory medium than water

Answer 1

Important respiratory gas is oxygen.  

The reasons why air is a better respiratory medium than water are as follows:

i) The amount of oxygen present per volume of air is greater than the amount present in water. At a given temperature and pressure, the amount of oxygen present in air is 20 times more than its amount in water.  

ii) Oxygen in air is present in the free form, while oxygen in water is bound to two molecules of hydrogen $(H_2O)$. Hence, the greater volume of water has to be taken in to receive the same volume of oxygen from the air.