One mole  of ${\mathrm{CH}}_4$ contains ____?

One mole of ${\mathrm{CH}}_4$ contains 4 moles of H atoms and one mole of C atoms. Mass of H atoms:

  $$\begin{gathered} \mathrm{Mass}=\mathrm{moles}\times \mathrm{atomic} \mathrm{mass} \\ =4 \mathrm{mol}\times 1 \mathrm{g}/\mathrm{mol} \\ =4 \mathrm{g} \end{gathered}$$