What is the energy in joules of a mole of photons associated with visible light of wavelength 486 nm?

Explanation:

The energy of a single photon is given by:

where

h is the Planck constant

c is the speed of light

is the wavelength

For the photon in this problem,

So, its energy is

One mole of photons contains a number of photons equal to Avogadro number:

So, the total energy of one mole of photons is

real, smaller and upside-down.   so the answer should be b.