A gaseous mixture of H₂, and CO₂ gas contains 66 mass % of CO₂. The vapour density of the mixture is:

No. of moles of CO₂ in 100 g mixture
$=\frac{66}{44}=1.5$
No. of moles of H₂ in 1oo g mixture
$\begin{array}{l}=\frac{34}{2}=17\\ {\mathrm{M}}_{\mathrm{average} }=\frac{100}{18.5}=5.40\\ \mathrm{V}.\mathrm{D}. =\frac{5.4}{2}=2.7\end{array}$