d
\({E_g} = \,\,2\,eV\,\, = \,\,2\,\, \times \,\,1.6\,\, \times \,\,{10^{ - 19}}\,\, = \,\,3.2\,\, \times \,\,{10^{ - 19}}\,J\)

\({E_g} = \,\,h{f}\)

\(\therefore \,{f}\,\, = \,\frac{{{E_g}}}{h}\,\, = \,\,\frac{{3.2\,\, \times \,\,{{10}^{ - 19}}}}{{6.62\,\, \times \,\,{{10}^{ - 34}}}}\,\,\,\,\,\,\therefore \,\,{f}\,\, = \,\,0.48\,\, \times \,\,{10^{15}}\,\, \approx \,\,\,5\,\, \times \,\,{10^{14}}\,Hz\)