1. Meaning of volume strength

For hydrogen peroxide, $x$-volume means:

1 volume of solution gives $x$ volumes of $O_2$ gas at NTP on decomposition.

So, 25-volume $H_2O_2$ means:

$1\,\text{L solution} \rightarrow 25\,\text{L } O_2 \text{ at NTP}$

2. Decomposition reaction

$2H_2O_2 \rightarrow 2H_2O + O_2$

From the equation:

• 2 mol$ $H_2O_2$ produce $1 mol $O_2$

At NTP, 1 mol gas occupies $22.4\,\text{L}$.

So, $22.4\,\text{L}$ of $O_2$ are produced by 2 mol of $H_2O_2$.

Mass of 2 mol $H_2O_2$:

$2 \times 34 = 68\,\text{g}$

Thus,

$22.4\,\text{L } O_2 \leftrightarrow 68\,\text{g } H_2O_2$

3. For 25 L of $O_2$

Required mass of $H_2O_2$ is:

$\text{Mass} = \frac{68}{22.4} \times 25$

$= 75.89\,\text{g} \approx 75\,\text{g}$

So, 1 L of marketed solution contains about 75 g of $H_2O_2$.

4. Check options

• A: 1 L marketed solution contains 75 g of $H_2O_2$ ✅
• B: 250 g in 1 L ❌
• C: 25 g in 1 L ❌
• D: 25 g in 100 mL means 250 g in 1 L ❌

5. Final answer

The correct option is:

$\boxed{\text{A}}$