c
$\mathrm{C}_{1}+\mathrm{C}_{2}=10$
$\frac{1}{2} \mathrm{C}_{2} \mathrm{V}^{2}=4 \times \frac{1}{2} \mathrm{C}_{1} \mathrm{V}^{2}$
$\therefore \quad \mathrm{C}_{2}=4 \mathrm{C}_{1}$
$\therefore \quad \mathrm{C}_{1}=2 \;and\; \mathrm{C}_{2}=8$
For series combination
$C_{e q}=\frac{C_{1} C_{2}}{C_{1}+C_{2}}=1.6$