Q 11-12-008NEETNEET 2020Top questionEasy
A cylinder contains hydrogen gas at pressure of $249$ kPa and temperature $27°$C. Its density is : ($R = 8.3\ \text{J mol}^{-1}\text{K}^{-1}$)
Answer: (B) $0.2\ \text{kg/m}^3$
Concept. From $PV = \dfrac{m}{M}RT$: $\rho = \dfrac{PM}{RT}$.
Step 1. Substitute. $M = 2 \times 10^{-3}$ kg/mol, $T = 300$ K:
$$\rho = \frac{249 \times 10^3 \times 2 \times 10^{-3}}{8.3 \times 300} = \frac{498}{2490} = 0.2\ \text{kg/m}^3$$
Answer. $0.2\ \text{kg/m}^3$ (Option B).
Solution by Sreeraj P, M.Sc Physics