The Mass Density of Normal Air at Room Temperature (293 $1.29 \mathrm{~kg} / \mathrm{m}^{3}$

Multiple Choice

The mass density of normal air at room temperature (293 K) is $1.29 \mathrm{~kg} / \mathrm{m}^{3}$ , and the average molecular mass of air is $29.0 \mathrm{u}$ . If the mean free path of an air molecule at room temperature is measured to be $111 \mathrm{~nm}$ , what is the average diameter of an air molecule?

A) $0.31 \mathrm{~nm}$
B) $0.23 \mathrm{~nm}$
C) $0.49 \mathrm{~nm}$
D) $0.26 \mathrm{~nm}$
E) $0.28 \mathrm{~nm}$
F) $0.56 \mathrm{~nm}$