An ion has 79 protons, 76 electrons, 116 neutrons. What is the correct formula of the ion?
First, get the element from the proton number. 79 protons corresponds to gold, Au.
A gold atom has originally 79 electrons. (Must be the same number as proton to be electrically neutral) Since now it only has 76 electrons, it has lost 3 electrons. It means now it has a state of +3.