What Part of an Atom ... ?

This may seem like a simple question, but if you put it to a nuclear physicist I'm sure he could come up with several answers.

The obvious answer is the neutron; but neutrinos also carry no charge, and for all I know there may well be others.

I can't think of any way of phrasing this question that's unambiguous and doesn't come down to an either/or. So best to avoid it, IMHO.