Find the mass of one molecule of methane, CH₄, in grams…

Step 1. Molar mass. $12\ \text{g/mol} + 4 \times 1\ \text{g/mol} = 16\ \text{g/mol}$.

Step 2. One molecule. $\dfrac{16\ \text{g}}{6.022 \times 10^{23}} = 2.66 \times 10^{-23}\ \text{g}$.