Number of neutrons present in 64 grams of methane is equal to (assume methane contains C-12  and  H-1  isotopes)

Number of fundamental particles in carbon = 6p + 6e + 6n

Number of fundamental particles in hydrogen = 1p + 1e

Number of fundamental particles in methane ( CH₄ ) = 10p + 10e + 6n

$$\begin{gathered} \mathrm{GMW} \mathrm{of} {\mathrm{CH}}_4\left(16\mathrm{g}\right) \mathrm{contains} 6{\mathrm{N}}_{\mathrm{A}} \mathrm{neutrons} \\ 64\mathrm{g} \mathrm{contains} \text{'}\mathrm{X}\text{'} \mathrm{neutrons} \\ \mathrm{X}=\frac{64}{16}\times 6{\mathrm{N}}_{\mathrm{A}}=24{\mathrm{N}}_{\mathrm{A}}=14.4\times {10}^{24} ; \end{gathered}$$