Specify the number of protons, neutrons, and electrons in the neutral atom bromine-80.

  80 equals the mass number. In the periodic table, the atomic number of Bromine is 35. The atomic number equals the number of protons.
  80-35= number of neutrons (mass-protons)
So, we have P=35   N=45
Furthermore, since the atom is neutral that must mean that the number of electrons equals the number of protons.
e=35