The symbol p represents the element phorphorus. this elements atomic number is 15. how many protrons and electrons are in a p-3 ion?

Phosphorus is element number 15, so the P atom has 15 protons and 15 electrons

for a total of + 15 + - 15 = 0 charge

P-3 has a charge of - 3 because it has attracted 3 electrons off a less electronegative atom.

Now, the P atom has 15 protons (+15) and 18 electrons (-18) which = - 3 net charge on the P-3 ion.