Answer
$$\begin{aligned}
\text { Number of molecules } =3.2 \times 10^{5} \text { molecules } \end{aligned}$$
Work Step by Step
We find:
$\begin{aligned}
\text { Number of molecules } &=(\text { molar conc. })(\text { volume })(6.022 \times
10^{23} \text {molecules}\cdot\operatorname{mol}^{-1} ) \\
&=\left(1.0 \times 10^{-3} \mathrm{mol} \cdot \mathrm{L}^{-1}\right)\left(5.24 \times 10^{-16} \mathrm{L}\right) \\
&\left(6.022 \times 10^{23} \text { molecules } \cdot \mathrm{mol}^{-1}\right) \\
&=3.2 \times 10^{5} \text { molecules } \end{aligned}$
