a
\( \mathrm{C}_{\mathrm{V}} \)\( =\frac{\mathrm{n}_1 \mathrm{C}_{\mathrm{r}_1}+\mathrm{n}_2 \mathrm{C}_{\mathrm{r}_2}}{\mathrm{n}_1+\mathrm{n}_2} \)
\( =\frac{2 \times \frac{3}{2} \mathrm{R}+6 \times \frac{5}{2} \mathrm{R}}{2+6} \)
\( =\frac{9}{4} \mathrm{R}\)