Explanation

(c) From Planck’s hypothesis, the energy of a photon of frequency $v$ is
$E = hv = \frac{hc}{\lambda}$
Where $c$ is speed of light and $\lambda$ the wavelength.
In the visible part, red colour has maximum wavelength
$\lambda = 8000\ \mathring{\mathrm{A}}$
$\therefore\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ E = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{8000 \times 10^{- 10}}$
Also, 1 eV= 1.6$\times 10^{- 19}$ J
$\therefore\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ E = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{8000 \times 10^{- 10} \times 1.6 \times 10^{- 19}}$
= 1.547 eV