Answer : The photon energy of this light in units of nanometers, (nm) is, 
Solution :
Formula used :

where,
E = energy of photon = 
h = Planck's constant = 
c = speed of light = 
= wavelength = ?
Now put all the given values in the above formula, we get:


conversion used : 
Therefore, the photon energy of this light in units of nanometers, (nm) is, 
Elements in group 1-2, 13-18, the number of valence electrons is related to the group number. For example, in the first group, the alkali metals there is one valence electron, however in group 13, there are 3 valence electrons. Valence electrons are also known as the outershell electrons.