Explanation:

\(E=n h v=n\left(\dfrac{h c}{\lambda}\right) \Rightarrow \dfrac{E}{t}=\left(\dfrac{n}{t}\right)\left(\dfrac{h c}{\lambda}\right)\)
\( \Rightarrow {10^{ - 7}} = \left( {\frac{n}{t}} \right)\frac{{6.626 \times {{10}^{ - 34}} \times 3 \times {{10}^8}}}{{5000 \times {{10}^{ - 10}}}}\)
\( \Rightarrow \frac{n}{t} = \frac{{5000 \times {{10}^{ - 10}} \times {{10}^{ - 7}}}}{{6.626 \times {{10}^{ - 34}} \times 3 \times {{10}^8}}} = 2.5 \times {10^{11}}\;{s^{ - 1}}\)