The number of protons is unique to each element, and is what gives the element its atomic number.
When the element has an equal number of protons and electrons, then the element is electrically neutral (since the positive and negative charges cancel each other out).
So the answer for this question would be protons, and then electrons.
Please see the attachments below structures of the 3 isomers of C8H18 that contain 3 methyl branches on the main chain, 2 of which are on the same carbon.
