Question

How is air dissolved in water different from ordinary air $?$

Answer 1

First we have to know that the amount of air that can be dissolved in water decreases with temperature and increases with pressure. As pressure increases dissolved oxygen will also increase in water. Ordinary air is a gas composed of Nitrogen, Oxygen, carbon dioxide and other various gases.

Complete answer:
Ordinary air composed of $78$ Nitrogen, $21$ oxygen, and $0.04$ carbon dioxide. The solubility of oxygen is higher than the solubility of other gases in water. Hence Nitrogen is less soluble in water when compared to carbon dioxide and Oxygen. Oxygen is more soluble in water than the air due to the formation of hydrogen bonding between the molecules of water. Thus, the concentration of oxygen in the water is more than that of in the air. Hence, the composition of air dissolved in water is different from ordinary air.
The composition of air dissolved in water is $33$ Oxygen when compared to $21$ of ordinary air. Nitrogen is $66$ when compared to $78$ of ordinary air and carbon dioxide is $1$ when compared to $0.04$ % in ordinary air.

Note:
Note that water at lower altitudes can hold more dissolved oxygen than water at higher altitudes. For both atmospheric and hydrostatic pressures, dissolved oxygen will increase as pressure increases. The percentage of oxygen dissolved in water depends upon various factors like temperature, pressure and dissolved salts.