
Final voltage after switch 2 is on: $V _{ f }=\frac{ C _1 V_1}{ C _1+ C _2}=\frac{2 V}{1 O }=0.2 V$
Final energy in both the capacitors,
$U _{ f }=\frac{1}{2}\left( C _1+ C _2\right) V _{ f }^2=\frac{1}{2} \times 10 \times\left(\frac{2 V}{10}\right)^2=0.2 V^2$
Therefore, energy dissipated $=\frac{ V ^2-0.2 V^2}{V^2} \times 100=80 \%$






