[LHM]

A sodium vapor street lamp emits yellow light with a wavelength of 589 nm. What is the energy of this light per mole of protons?

A) 3.37*10^-16 kJ/mol
B) 2.35*10^-13 kJ/mol
C) 0.201 kJ/mol
D) 203 kJ/mol

I got D by doing: (2.998 m*s^-1)/(589*10^-9)*6.626*10^-34 J*s*6.022*10²³=203 kJ/mol. The answer is B though, why?

[Borek]

A sodium vapor street lamp emits yellow light with a wavelength of 589 nm. What is the energy of this light per mole of protons?

Per mole of protons? Or photons?

If photons - correct answer seems to be D, and your calculations are correct - even if c is not 2.998 m/s.

[LHM]

Well, it does say protons. What do you do differently then if it's protons instead of photons? Do you have to multiply by 11 somewhere?

[Borek]

If it says protons - there is no information about proton energy, so it can't be solved.

However, in the case of photons - there is a known formula linking photon's frequency with its energy, there is also a known formula linking photon's frequency with its wavelength.