Question

Why is the percentage of oxygen dissolved in water more than the percentage of oxygen dissolved in ordinary air?

Answer 1

Air dissolved in water contains high percentage of oxygen because solubility of oxygen gas in water is more than nitrogen and other gases present in the air. This is due to the small size of oxygen as compared to nitrogen due to which it easily gets trapped inside the vacant space between H2O molecules.
Moreover, hydrogen bonding between water molecules and oxygen takes place which increases its solubility. Nitrogen also shows hydrogen bond formation but to a lesser extent as compared to oxygen.