Protons have a positive charge, giving an element it's identity (defined by the Atomic Number, or how many protons it has).
Electrons have a negative charge, giving an element it's reactivity (~balanced number of protons and electrons in an atom).
Neutrons have a neutral charge, or "no" charge. The amount of neutrons in an element define the element's Atomic Mass (~sum of protons and electrons in the atom).
Your answer is Neutrons, since Protons and Electrons both have a charge.
