Electron configuration for phosphorus is 1s2 2s2 2p6 3s2 3p3. So the number of electron must be 15 , right ? But , what if m = 1 ? Does it effect the number of electron ?

Answer 1

The atomic number of P is 15 which means P has 15 protons; therefore, the number of electrons for a neutral P atom MUST be 15. m being 1 affects the energy level of one or more of the electrons (and of course the P atom) but it doesn't change the number of electrons from 15.