The volume(in ml) of oxygen liberated from 15 ml of 20 volume H₂O₂ is

 

Quantity ofH₂O₂=15ml and volume of H₂O₂=20

We know that 20 volume ofH₂O₂means 1 liter of this solution will give 20 liter of oxygen at N.T.P. 

Since, oxygen liberated from 1000 ml (1 liter) of H₂O₂=20liter, 

Therefore oxygen liberate from 15 ml of H₂O₂=$\frac{20}{1000}\times 15=0.3\mathrm{lit}.=300\mathrm{ml}$