How many protons electrons and neutrons does the isotope nitrogen 15 have

The atomic number ofN157 
The number of protons is 7
The number of electrons is 7
The number of neutrons is 8

The atomic number of Nitrogen is 7 because Nitrogen has 7 protons. 
The seven protons attract 7 electrons in the ground state.

If the atom had fewer or more than 7 protons the atom would not be Nitrogen.

The mass of the atom is the sum of protons and neutron. so

p + n = mass ( protons (p) and neutrons(n) both have an atomic mass of one

7 + n = 15 subtract 7 from both sides

7−7+n=15−7

n = 8

it's c. elements are placed in rows based on how may valencies electrons have.