The neutral particle in an atom.

Atoms consist of three types of sub-atomic particles:

1. Protons: Protons are positively charged particles present in the nucleus of an atom.
2. Electrons: Electrons are negatively charged particles present in the shells of an atom.
3. Neutrons: Neutrons are the electrically neutral particles present in the nucleus of an atom.

Thus, the neutral particle in an atom is neutron.