Question

How 23% of the air can be oxygen

Answer 1

Consider we have 100 g of air.  

Mass of oxygen in 100 g of air = 23 g

Mss of nitrogen in 100 g of air = 77 g

Molar mass of Oxygen = 32 g

1 mole of oxygen or 32 g of Oxygen occupy 22.4 L volume so 23 g of oxygen will occupy 22.432×23

= 16.1 L

Similarly, 28 g of Nitrogen occupy 22.4 L, so 77 g of Nitrogen will occupy 22.428×77

= 61.6 L

Total volume of air = 16.1 + 61.6

= 77.7 L

% by volume of Oxygen = 16.177.7×100

= 20.7 %

Answer 2

because somewhat 70% are nitrogen and 2% are other gases