The valence electron in potassium requires #6.95 xx 10^-19# #"J"# of energy to be removed. What frequency of light can do this? What type of electromagnetic radiation could do this?
Very blue visible photons or UV photons.
This electron in the
Now, referring to the EMR diagram that I gaurantee you most people don't have absolutely memorized:
This energy corresponds with the frequency of very blue photons (visible) or UV photons.