Answer
$1.05\times10^{-10}$ m
Work Step by Step
750 torr = 99991.8 Pa
-40$^{\circ}$C = 233.15 K
Boltzmann constant $k=1.38\times10^{−23}$
Diameter of an Ar atom calculated $λ_{Ar}=8.3\times10^{-9}m$
Free path equation $λ=\frac{kT}{\sqrt 2 \timesπ\times d^{2}\times p}$
$λ_{Ar}=\frac{1.38\times10^{-23}\times 233.15}{\sqrt 2 \timesπ\times (8.3\times10^{-9})^{2}\times99991.8}$
$λ_{Ar}=1.05\times10^{-10}m$
