'25 volume' hydrogen peroxide means

Determine what "25 volume" hydrogen peroxide means in terms of mass of $$H_2O_2$$ per litre.

"25 volume" $$H_2O_2$$ means 1 L of this solution releases 25 L of $$O_2$$ at STP upon complete decomposition.

The decomposition reaction is $$2H_2O_2 \rightarrow 2H_2O + O_2$$.

Since 1 mole of $$H_2O_2$$ produces $$\frac{1}{2}$$ mole of $$O_2$$, which corresponds to 11.2 L at STP, the volume strength is $$11.2 \times M$$ where M is the molarity of $$H_2O_2$$. Equating this to 25 gives $$25 = 11.2 \times M$$, so $$M = \frac{25}{11.2} = 2.232$$ mol/L.

The molar mass of $$H_2O_2$$ is 34 g/mol, so the mass per litre is $$2.232 \times 34 \approx 75.9$$ g, which is approximately 75 g.

Comparing with the given options, 250 g/L (Option A) is too high; 75 g/L (Option B) matches our calculation $$\checkmark$$; 25 g per 100 mL = 250 g/L (Option C) is too high; and 25 g/L (Option D) is too low. Thus the correct answer is Option B.