Question

A glass tube of volume 112 ml containing a gas is partially evacuated till the pressure in it drops to $3.8\times {10}^{-5}$ torr at $0^{0}C$. The number of molecules of the gas remaining in the tube is

• A. $3.7\times {10}^{17}$
• B. $1.5\times {10}^{14}$
• C. $4.5\times {10}^{18}$
• D. $1.5\times {10}^{19}$

Answer 1

The correct option is B $1.5\times {10}^{14}$

PV=nRT
$n=\frac{PV}{RT}=\frac{3.8\times {10}^{-5}\times 112\times {10}^{-3}}{62.4\times 273}$
$=0.02461\times {10}^{-8}mol$
No. of molecules = $0.02461\times {10}^{-8}mol$
$=1.5\times {10}^{14}$