Previous Year NEET Question- Kinetic Theory L-2

Question: A given sample of an ideal gas occupies a volume $V$ at a pressure $p$ and absolute temperature $T$. The mass of each molecule of the gas is $m$. Which of the following gives the density of the gas? [NEET 2016]#

A) $p /(k T)$

B) $\mathrm{pm} /(\mathrm{k} T)$

C) $p /(k T V)$

D) $\mathrm{mkT}$

Answer: $\mathrm{pm} /(\mathrm{k} T)$#

Solution:#

As we know, that Pressure, $p=\frac{1}{3} \cdot \frac{n m}{V} v_{\text {rms }}^2$ $\because \mathrm{nm}=$ number of moles, $V=$ volume of the gas $$ \begin{alignedat} & \therefore \frac{m n}{V}=\text { density of the gas. Thus, } \ & p=\frac{1}{3} \rho \frac{3 R T}{M_0}=\frac{\rho R T}{M_0} \ & \quad\left(\because v_{\text {rms }}=\sqrt{\frac{3 R T}{M_0}}\right) \ & \rho=\frac{p M_0}{R T}=\frac{p m N_A}{k N_A T} \ & \quad\left[\because R=N_A k \text { and } M_0=m N_A\right] \ & \rho=\frac{p m}{k T} \quad \end{aligned} $$