$$2.0$$ g of $$H_2$$ gas is adsorbed on $$2.5$$ g of platinum powder at $$300$$ K and $$1$$ bar pressure. The volume of the gas adsorbed per gram of the adsorbent is ______ mL
(Given : $$R = 0.083$$ L bar K$$^{-1}$$ mol$$^{-1}$$)

We need to find the volume of gas adsorbed per gram of the adsorbent.

Find the number of moles of $$H_2$$ gas.

Molar mass of $$H_2$$ = 2 g/mol

$$n = \frac{2.0}{2} = 1 \text{ mol}$$

Calculate the volume of gas using the ideal gas equation.

$$PV = nRT$$

$$V = \frac{nRT}{P} = \frac{1 \times 0.083 \times 300}{1}$$

$$V = 24.9 \text{ L} = 24900 \text{ mL}$$

Find volume per gram of adsorbent.

Mass of adsorbent (platinum powder) = 2.5 g

$$\text{Volume per gram} = \frac{24900}{2.5} = 9960 \text{ mL}$$

Therefore, the volume of gas adsorbed per gram of the adsorbent is $$\textbf{9960}$$ mL.