meanings of the various table numbers given in the the text calculate how many neutrons there are in a phosphours atom.
As your reading material says….
Atomic weight = Protons + Neutrons (since electrons have a negligible mass). So find the atomic # (which is the # of protons) and subtract that from the weight.
P=atomic number 15 (15 protons
P atomic weight 31 (15 protons +16 NEUTRONS