# The atomic number of nitrogen is 7. How many protons, neutrons, and electrons make up an atom of nitrogen-15?

By definition, if $Z$, the atomic number $=$ $7$, then there are 7 protons, 7 electrons, and 8 neutrons!
Electrons have negligible mass; the mass number depends on the number of protons contained within the nucleus, PLUS the number of neutrons. Given that we have ""^15N, there must be 8 neutrons contained within the nucleus. Capisce?