a
As $q=C V$
Hence slope of graph will give capacitance. Slope will be more in parallel combination. Hence capacitance in parallel should be $50\, \mu \mathrm{F}$ and in series combination must be $8\, \mu F$. Only in option $40\, \mu F$ and $10\, \mu \mathrm{F}$.
$C_{Parallel} $ $=40+10=50 \,\mu F$
$C_{series}$ $=\frac{40 \times 10}{40+10}=8\, \mu \mathrm{F}$