d
To get effective capacitance of \(6\, \mu F\) two capacitors of \(4\, \mu \mathrm{F}\) each connected in series and one of \(4\, \mu \mathrm{F}\) capacitor in parallel with them.

Two capacitances in series

\(\therefore \frac{1}{C}=\frac{1}{C_{1}}+\frac{1}{C_{2}}=\frac{1}{4}+\frac{1}{4}=\frac{1}{2}\)

\(1\) capacitor in parallel 

\(\therefore \) \(C_{\mathrm{eq}}=C_{3}+C=4+2=6\, \mu \mathrm{F}\)