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

Multiple Choice

The mass density of normal air at a certain temperature is $1.29 \mathrm{~kg} / \mathrm{m}^{3}$ . If the average molecular mass of air is $29.0 \mathrm{u}$ , how many air molecules are in spherical balloon of radius $15.0 \mathrm{~cm}$ ?

A) $3.8 \times 10^{23}$
B) $2.5 \times 10^{25}$
C) $3.3 \times 10^{25}$
D) $8.5 \times 10^{23}$
E) $1.1 \times 10^{24}$
F) $9.8 \times 10^{24}$