c
Total energy per sec. \(=50\, {~J}\)

\(50=\frac{{n} \times 6.63 \times 10^{-34} \times 3 \times 10^{8}}{795 \times 10^{-9}}\)

\({n}=1998.49 \times 10^{17}[{n}={no} .\) of photons per second \(]\)

\(=1.998 \times 10^{20}\)

\(\simeq 2 \times 10^{20}\)

\(={x} \times 10^{20}\)

\({x}=2\)