(a) The energy stored is given by
$E = \frac{1}{2}CV^{2}$
When capacitors are connected in parallel, resultant capacitance is
$C^{'} = \ C_{1} + C_{2}$
$= 2\mu F + 2\mu F = 4\mu F$
$V = 100$ volt
$\therefore = \frac{1}{2} \times 4 \times 10^{- 6} \times (100)^{2}\ $
$E = 0.02$J