Volume of air = 1200 ml
Further explanation
Given
20% Oxygen in air
240 ml Oxygen
Required
Volume of air
Solution
The concentration of a substance can be expressed in several quantities such as moles, percent (%) weight / volume,), molarity, molality, parts per million (ppm) or mole fraction. The concentration shows the amount of solute in a unit of the amount of solvent
240 ml = 20% Oxygen
volume of air :
= 100%/20% x 240 ml
= 1200 ml
