The volume of oxygen liberated from 15 ml of 20 volume H₂O₂ is

Quantity of H₂O₂ = 15 ml and volume of H₂O₂ = 20. We know that 20 volume of H₂O₂ means 1 litre of this solution will give 20 litres of oxygen at N.T.P.

Since, oxygen liberated from 1000 ml (1 litre) of H₂O₂ = 20 litre, therefore oxygen liberate from 15 ml of H₂O₂ = $\frac{20}{1000} \times 15 = 0.3 \mathrm{litre} = 300 \mathrm{ml}$