(d) Equivalent capacitance $= \frac{2 \times 3}{2 + 3} = \frac{6}{5}\mu F$
Total charge by $Q = CV = \frac{6}{5} \times 1000 = 1200\mu C$
Potential $(V)$ across $2\mu F$ is $V = \frac{Q}{C} = \frac{1200}{2} = 600volt$
$\therefore$ Potential on internal plates $= 1000 - 600 = 400\ V$