Which of the following particles has zero charge ?

The correct answer is B) Neutrino. A neutrino is an electrically neutral lepton, so its charge is zero. It takes part only in weak nuclear and gravitational interactions, which is why it passes through matter almost unnoticed.

• A) Positron: It is the antiparticle of the electron, with charge +1e (+1.6 × 10^-19 C). Being antimatter does not make it neutral.
• C) Electron: It carries charge -1e, the basic unit of negative charge in atoms.
• D) Alpha particle: It is a helium-4 nucleus with 2 protons and 2 neutrons, so its charge is +2e. The neutrons are neutral, but the protons are not.

The core concept is electric charge and its classification among leptons, hadrons and bosons. For Mains GS-III (science and technology), neutrino oscillation is a good link. It showed that neutrinos have a small but non-zero mass, which earned the 2015 Nobel Prize in Physics. Note that neutrinos being neutral does not mean they are massless; that is a separate point.

Trap: Aspirants often confuse 'neutral' with 'no interaction' or assume the alpha particle is neutral because helium is an inert gas. The alpha particle is a doubly charged ion-like nucleus.