2 N means 2 g eqwt in 1 L solution.
N= weight/eq.wt (eq wt for hydrogen peroxide = 17 g)
Therefore, $2 = \large\frac{wt}{17}$ or $wt = 2 \times 17 = 34 g$
Now, from equation we know that 68 g of $H_2O_2$ gives 22.4 L of Oxygen.
Therefore, 25.5 g of Hydrogen peroxide gives- $\large\frac{22.4 \times 34}{68} = 11.2 L$