Answer
$6.6\times10^{-10}$
Work Step by Step
150 torr = 19998.4 Pa
20$^{\circ}$C = 293.15 K
Boltzmann constant $k=1.38\times10^{−23}$
Diameter of an Ar atom calculated $λ_{Ar}=8.3\times10^{-9}m$
Free path equation calculated by $λ=\frac{kT}{\sqrt 2 \timesπ\times d^{2}\times p}$
$λ_{Ar}=\frac{1.38\times10^{-23}\times 293.15}{\sqrt 2 \timesπ\times (8.3\times10^{-9})^{2}\times19998.4}$
$λ_{Ar}=6.6\times10^{-10}$
