Answer
$3.3 \times 10^{13}$ molecules
Work Step by Step
Solve the ideal gas equation to find the number moles of gas,
$PV = nRT$ where $R$ is the universal gas constant
$n=\frac{PV}{RT} = \frac{1.0 × 10–3 Torr \times 1.00 \times 10^{-3}L}{62.3637L⋅Torr⋅mol^{-1}K^{-1} \times (273+20)K}=5.460 \times 10^{-11}mol$
One mole of gas molecules is equal to $6.022 \times 10^{23}$ number of molecules. Hence total number of gas molecules can be found as,
$5.460 \times 10^{-11}mol \times 6.022 \times 10^{23}mol^{-1} = 3.3 \times 10^{13}$
