Molar mass of methane,
\begin{aligned}H _{4}=[12+(1 \times 4)] & \Rightarrow 16 gmol ^{-1} . \\
\text { Mole of methane } & \Rightarrow \frac{8 g }{16 g mol } \\
& \Rightarrow 0.5 mol
\end{aligned}
Number of molecules
\begin{aligned}
&=\left(\begin{array}{c}
\text { number } \\
\text { of moles }
\end{array}\right) \times 6.02 \times 10^{23} \\
&0.5 \times 6.02 \times 10^{23} \Rightarrow 3.01 \times 10^{23}
\end{aligned}