Initial stored energy =Energy‌of‌capacitor‌1 =
1
2
C1V12 =
1
2
×500×10−12×(100)2...[∵C1=500pFV1=100V] ‌=250×10−12×104=250×10−2×10−6 ‌=2.5µJ When both capacitors are joined, common potential of combination is V‌common ‌=V=‌
Q1+Q2
C1+C2
‌ or ‌V=‌
C1V1+C2V2
C1+C2
or V=
500×10−12×100
2×500×10−12
=50V Final stored energy =
1
2
(C1+C2)V2 =
1
2
×2×500×10−12×(50)2 =500×10−12×2500 =125×10−8 =1.25×10−6J =1.25µJ Loss of energy, ∆U=Final‌energy−Initial‌energy =25−1.25µj=1.25µj (No option is matching)