$\left({h}=6.63 \times 10^{-34}\, {Js}, {c}=3.00 \times 10^{8} \,{~ms}^{-1}\right)$
$=0.1\, {sec} \cdot \times 10^{-3} \,\frac{{J}}{{s}}$
$=10^{-4}\, {~J}$
If $'n'$ photons of $\lambda=1000\, {~nm}$ are emitted,
$\text { then ; } 10^{-4}={n} \times \frac{{hc}}{\lambda}$
$\Rightarrow 10^{-4}=\frac{{n} \times 6.63 \times 10^{-34} \times 3 \times 10^{8}}{1000 \times 10^{-9}}$
$\Rightarrow {n}=5.02 \times 10^{14}=50.2 \times 10^{13}$
$\Rightarrow 50$ (nearest integer)
$4s$ $3d$