First line: The atomic number is the whole number on the periodic table so atomic number 35 means the element is bromine. Thus the element symbol is Br. The atomic number is also the number of protons in the isotope so the number of protons is 35. The mass number is the sum of protons and neutrons in the isotope so the mass number is 35+46 or 81. The mass number gives you the top left number on the nuclear symbol (it will look the same as the one below it except the 79 is an 81). Lastly, the number of electrons is equal to the number of protons in a neutral atom so 35 electrons.