a
\(E \Rightarrow \frac{1}{2}( KC ) v ^{2}\)
\(\therefore \%\) change
\(\Rightarrow \frac{\frac{1}{2} K _{2} CV ^{2}-\frac{1}{2} K _{1} CV ^{2}}{\frac{1}{2} K _{1} CV ^{2}}=\frac{ K _{2}- K _{1}}{ K _{1}} \times 100\)
\(\Rightarrow \frac{15-10}{10} \times 100=50 \%\)