Which of the following particles has zero charge?
- (a)Positron
- (b)Neutrino
- (c)Electron
- (d)α-particle
Correct — B, the neutrino. A neutrino is an electrically neutral elementary particle (a lepton): it carries zero charge and has an extremely tiny mass, interacting only through the weak nuclear force and gravity. Of the four options it is the only chargeless one — the positron carries +1e, the electron −1e, and the α-particle +2e.
- (a)Positron — The positron is the antiparticle of the electron and carries a positive charge of +1e (equal in magnitude to the electron's), so it is not chargeless.
- (c)Electron — The electron carries a negative charge of −1e — the fundamental unit of negative charge — so it is not neutral.
- (d)α-particle — An alpha particle is a helium-4 nucleus (2 protons + 2 neutrons) and carries a charge of +2e, so it is not chargeless.
Electric charge of subatomic particles is quantised in units of the elementary charge e. Charged particles (electron −1, proton/positron +1, alpha +2) respond to electric and magnetic fields; neutral particles do not. The neutrino is a neutral, near-massless lepton produced in weak-interaction processes such as beta decay, which is why it is so difficult to detect.
Screen each option by charge: positron +1, electron −1, alpha +2, neutrino 0 — only the neutrino is neutral. Do not confuse 'neutrino' with 'neutron': both are neutral, but the neutron is a composite nucleon while the neutrino is a light lepton.
- Neutrino — neutral, near-massless lepton; interacts only via the weak force and gravity.
- Positron = +1e (antielectron); electron = −1e.
- Alpha particle = helium nucleus, charge +2e.
- Neutrinos are emitted in beta decay and are extremely penetrating (they rarely interact).
Only the neutrino carries zero electric charge.
- Confusing the neutrino (light lepton) with the neutron (composite nucleon) — both are neutral.
- Assuming the positron is neutral because it is an 'anti' particle — it is +1e.
UPSC/UPPSC ask for the charge/mass of a named particle, match particles to a property (mass/charge/spin), or test S&T current affairs like the India-based Neutrino Observatory.
Match List I (Characteristic) with List II (Particle) and select the correct answer: List I: I. Zero mass II. Fractional charge III. Fractional spin IV. Integral spin List II: A) Positron B) Neutrino C) Quark D) Phonon
- (a) I-B, II-C, III-A, IV-D
- (b) I-C, II-B, III-D, IV-A
- (c) I-B, II-C, III-D, IV-A
- (d) I-C, II-B, III-A, IV-D
Answer(a) I-B, II-C, III-A, IV-D
Same concept — properties (mass/charge/spin) of elementary particles, including the neutrino and positron that appear in this question.
The alpha particle carries two positive charges. Its mass is very nearly equal to that of
- (a) two protons
- (b) an atom of helium
- (c) sum of masses of two positrons and two neutrons
- (d) two positrons as each positron carries a single positive charge
Answer(b) an atom of helium
Tests the charge and identity of the α-particle — one of the options here — confirming it carries +2e (a helium nucleus), i.e. it is not chargeless.
- practice — not a real PYQ
Which of the following is an electrically neutral, nearly massless elementary particle emitted during beta decay?
- (a)Proton
- (b)Neutrino
- (c)Positron
- (d)Muon
Answer(b) Neutrino — neutral and near-massless, unlike the charged proton, positron and muon.
- practice — not a real PYQ
The India-based Neutrino Observatory (INO) was planned with its detector placed:
- (a)on a high mountain peak
- (b)in outer space
- (c)deep underground, inside a mountain
- (d)on the ocean surface
Answer(c) deep underground — surrounding rock screens out background radiation so rare neutrino events can be recorded.