Neutron is defined as?

• A. A sub-atomic particle with no charge and about the same mass as a proton.
• B. A positively charged particle in the nucleus.
• C. A negatively charged particle with tiny mass.
• D. A particle that orbits the nucleus with massless property.

Answer: (A)

Neutrons are neutral nucleons in the nucleus. They have no electric charge, which means they don’t contribute to the electrostatic repulsion between protons, and they have a mass that's essentially the same as a proton (about 1 atomic mass unit). This combination—neutral charge and roughly equal mass to the proton—lets neutrons participate in the strong nuclear force that binds nuclei together without adding electrical repulsion. The other descriptions describe particles that either carry charge, like protons or electrons, or suggest a particle that orbits the nucleus with properties that don’t match a neutron, so they don’t fit.