Wave length range of visible spectrum extends from 400 nm to 750 nm. The frequency of U.V rays will be ---- s^-1

$$\begin{gathered} \mathrm{\nu }=\frac{\mathrm{C}}{\mathrm{\lambda }}=\frac{3\times {10}^8 \mathrm{m}/\mathrm{s}}{400\times {10}^{-9} \mathrm{m}}=7.5\times {10}^{14}\mathrm{Hz} --- \mathrm{Violet} \\ \mathrm{\nu }=\frac{\mathrm{C}}{\mathrm{\lambda }}=\frac{3\times {10}^8 \mathrm{m}/\mathrm{s}}{750\times {10}^{-9} \mathrm{m}}=4\times {10}^{14}\mathrm{Hz} --- \mathrm{Red} \\ \mathrm{Frequency} \mathrm{of} \mathrm{U}.\mathrm{V} \mathrm{rays} \mathrm{must} \mathrm{be} \mathrm{greater} \mathrm{than} 7.5\times {10}^{14} \mathrm{Hz}. \end{gathered}$$