Mass of 0.1 mole of methane is

$\text{ No. of mole }=\frac{\text{ mass of substance }}{\text{ molecular mass of substance }}$
$0.1=\frac{\mathrm{W}}{{\mathrm{M}}_{{\mathrm{CH}}_4}};0.1=\frac{\mathrm{W}}{16}\left(\because {\mathrm{M}}_{{\mathrm{CH}}_4}=16\right)\Rightarrow \mathrm{W}=1.6 \mathrm{gm}$