a
\(Q = CV =600 \times 10^{-12} \times 200=12 \times 10^{-8} C\)

\(\text { Initial energy }=\frac{1}{2} CV ^2\)

\(=\frac{1}{2} \times 600 \times 10^{-12} \times(200)^2=12\,\mu J\)

When connected to another uncharged capacitor

Charge will be equally distributed on identical capacitor

\(Q ^{\prime}=\frac{ Q }{2}=6 \times 10^{-8}\)

Final energy \(=2 \times \frac{ Q ^{\prime 2}}{2 C }=\frac{ Q ^{\prime 2}}{ C }\)

\(\frac{\left(6 \times 10^{-8}\right)^2}{600 \times 10^{-12}}=6\,\mu J\)

Energy lost = Initial energy - Final energy

\(=(12-6)\,\mu\, J =6\, \mu\, J\)