Answer
a. 1.7 eV
b. 3.1 eV
Work Step by Step
a. The minimum energy is the minimum energy of a single photon of visible light. Red light is the least energetic, and has a wavelength of about 750 nm.
$$E= hf =\frac{hc}{ \lambda}$$
$$=\frac{( 6.63\times10^{-34}J \cdot s)(3.00\times10^8m/s)}{750\times10^{-9}m}\frac{eV}{1.60\times10^{-19}J}$$
$$=1.7 eV$$
b. The maximum energy that triggers a reaction is the energy of a single photon of violet light. Violet light is the most energetic type of visible light, and has a wavelength of about 400 nm.
$$E= hf =\frac{hc}{ \lambda}$$
$$=\frac{( 6.63\times10^{-34}J \cdot s)(3.00\times10^8m/s)}{400\times10^{-9}m}\frac{eV}{1.60\times10^{-19}J}$$
$$=3.1 eV$$
