Separation between plates of a parallel plate capacitors is 'd'. It is charged a battery then disconnected ,a dielectric slab of thickness $\large\frac{d}{3}$ and constant 3 is introduced in it . The fractional change in energy .

Question

$\begin{array}{1 1} \large\frac{-2}{9} \\ \large\frac{+2}{9} \\\large\frac{-4}{9} \\ \large\frac{4}{9} \end{array} $