The power obtained in a reactor using U^ 235 disintegration is 1000...

Let assume power $P=1000 \mathrm{~W}$ Energy per hour $=1000 \times 3600 \mathrm{~J}$ Energy per fission $=200 \mathrm{MeV}=200 \times 1.6 \times 10^{-13} \mathrm{~J}\therefore$ Number of fission per hour $n=\frac{1000 \times 3600}{200 \times 1.6 \times 10^{-13}}$$\begin{aligned} & \text{Number of mole per hour }=\frac{n}{N} \\ & \therefore \text{ Mass per hour }=\frac{n}{N} \times 235 \end{aligned}$$\begin{aligned} & =\frac{1000 \times 3600 \times 235}{200 \times 1.6 \times 10^{-13} \times 6.02 \times 10^{23}} \\ & =43.9 \times 10^{-6} \mathrm{~g} \end{aligned}$$$This$43.9 \times 10^{-6} \mathrm{~g}$ is nearest value of 40 micro gram so option (b) is correct.