A gaseous mixture contains ${\mathrm{CH}}_4\mathrm{and}{\mathrm{C}}_2{\mathrm{H}}_6$ in equimolecular proportion. The weight of 2.24 litres of this mixture at NTP is

 Equimolecular proportion means both gases occupied equal volume

Volume of the mixture = 2.24l

volume of   ${\mathrm{CH}}_4=\frac{2.24}{2}=1.12\mathrm{L}$

$\begin{array}{l}22.4\mathrm{L}{\mathrm{CH}}_4\mathrm{has}\mathrm{mass}=16\mathrm{g}\\ 1.12\mathrm{L}{\mathrm{CH}}_4\mathrm{has}\mathrm{mass}=\frac{16}{22.4}\times 1.12=0.8\mathrm{g}\\ \mathrm{For}{\mathrm{C}}_2{\mathrm{H}}_6\\ 22.4\mathrm{L}{\mathrm{C}}_2{\mathrm{H}}_6\mathrm{has}\mathrm{mass}=30\mathrm{g}\\ 1.12\mathrm{L}{\mathrm{C}}_2{\mathrm{H}}_6\mathrm{has}\mathrm{mass}\frac{30}{22.4}\times 1.12=\frac{3.0}{2}=1.5\mathrm{g}\\ \mathrm{Total}\mathrm{mass}=1.5\mathrm{g}+0.8\mathrm{g}=2.3\mathrm{g}.\end{array}$