The percentage of oxygen in NaOH is ?

The percentage of oxygen in air is-

Give reasons for the following: The percentage of oxygen, in air dissolved in water, is higher than the percentage of oxygen in ordinary air.

The percentage of oxygen in CH_(2) O is

The percentage of oxygen in CH_(2) O is

The percentage of oxygen in heavy water is

The percentage of oxygen in a compound is determined by

What is the percentage of oxygen in atmosphere ?