The volume of dry oxygen liberated at STP when 1 ml of 2 Normal H₂O₂ solution is heated is 

$2 = \frac{\mathrm{Vol}.\mathrm{strength} }{5.6}$

Volume strength = 2 $\times$5.6 = 11.2

Volume of dry O₂ liberated at STP = ml of H₂O₂ taken$\times$ Volume strength = 1$\times$11.2 = 11.2 ml