d
Energy required to break one \(\mathrm{Cl}_{2}\) molecule \(=\frac{242 \times 10^{3}}{6.02 \times 10^{23}} \mathrm{\,J}\)

As \(\mathrm{E}=\frac{h c}{\lambda}\)

So \(\lambda=\frac{h c}{E}\)

\(=\frac{6.626 \times 10^{-34} \times 3 \times 10^{8} \times 6.02 \times 10^{23}}{242 \times 10^{3}}\)

\(=494 \times 10^{-9} \mathrm{m}\)

\(=494 \mathrm{\,nm}\)