Question

Two identical flasks $X$ and $Y$ contain $64$g of methane and $100$g of an unknown gas $A_2$ respectively at $2$ atm and $300$K. The vapour density of the gas $A_2$ will be:

• A. $50$
• B. $37.5$
• C. $25$
• D. $12.5$

Answer 1

Answer: (D)

$12.5$

$PV=nRT$, Here $P,V$ & $T$ are constants

$\therefore n$ is constant Molecular mass of methane= $16g$

Now, $\frac{64}{16}=\frac{100}{M_{A_2}}$

$\Rightarrow M_{A_2}=\frac{100\times 16}{64}=25$

$\therefore$ Vapour density= $\frac{\text{Molecular mass}}{2}$

$=\frac{25}{2}$

$=12.5$