Question

Oxygen is present in a litre flask at a pressure of $7.6 \times 10^{-10}\, mm \,Hg$. The number of oxygen molecules in the flask at $0^{\circ}C$ is:

• A. $2.7 \times 10^{9}$ molecules
• B. $2.7 \times 10^{10}$ molecules
• C. $2.7 \times 10^{11}$ molecules
• D. $2.7 \times 10^{12}$ molecules

Answer 1

Answer: (B)

$PV= nRT$
$n=\frac{PV}{RT} $
$\Rightarrow \frac{7.6\times10^{-10}}{760}\times\frac{1}{0.082\times273}$
$n=0.0446\times10^{-12}$
The number of oxygen molecule
$=0.0446 \times10^{-12} N_{A}$
$\Rightarrow 2.7\times10^{10}$