Answer
5.50 eV
Work Step by Step
The minimum-frequency (i.e., maximum-wavelength) photon that enables conduction has an energy equal to the energy gap.
$$E_g=hf=\frac{hc}{\lambda}$$
$$=\frac{(6.63\times10^{-34}J \cdot s)(3.00\times10^8m/s)}{(1.60\times10^{-19}J/eV)(226\times10^{-9}m)}$$
$$=5.50 eV$$
