JEE Main 2012 — Capacitance Question with Solution

A series combination of $n_1$ capacitors, each of capacity $C_1$ is charged by source of potential difference $4\mathrm{V}$. When another parallel combination of $n_2$ capacitors each of capacity $C_2$ is charged by a source of potential difference $V$, it has the same total energy stored in it as the first combination has. The value of $C_2$ in terms of $C_1$ is then