(d) Energy released in the fission of one nucleus $= 200\ MeV$
$= 200 \times 10^{6} \times 1.6 \times 10^{- 19}J = 3.2 \times 10^{- 11}J$
$P = 16kW = 16 \times 10^{3}watt$
Now, number of nuclei required per $second$
$n = \frac{P}{E} = \frac{16 \times 10^{3}}{3.2 \times 10^{- 11}} = 5 \times 10^{14}$