उत्तर : 3. "न्यूट्रॉन"
व्याख्या :

Atom: The smallest particle of any element which has all the chemical and physical properties of that element,

Is called atom. An atom consists of three subatomic particles: the electron, the proton, and the neutron. Protons and neutrons reside in the nucleus and electrons move around the nucleus on a particular path.

The electron has a negative charge on itself and the proton has a positive charge.

The neutron is neutral.