Which of the following is correct regarding the electron energy shell configuration of a phosphorus atom (atomic number 15)?
A. 2, 5, 5
B. 2, 8, 5
C. 2, 8, 18
D. 10, 5
E. None of the above

C. 2, 8, 18
This is the most understanding.

C. seems the most accurate

Because electrons have negligible mass, to account for the mass of the isotope, there must be 16 neutrons, 16 neutrally charged, massive, fundamental particles present in the sulfur nucleus. and thus finally, if we have the 32s2− ion, there are 18 electrons, 16 protons, and 16 neutrons.