NDA (I) 2025 GAT Q73: Which one of the following particles in the nucleus of an

Q: What is the answer to NDA (I) 2025 GAT Q73?

D. Correct — D, Neutron. James Chadwick discovered the neutron in 1932 by bombarding beryllium with alpha particles and detecting a neutral particle of roughly proton mass. The neutron sits in the nucleus alongside the proton and carries no charge, which is why it had eluded earlier experiments. (Provisional — pending the official UPSC key.)

NDA (I) 2025 General Ability Test · Question 73 of 150

Question text verified against the official NDA question paper.

Provisional answers. UPSC has not yet released the official NDA 2025 answer key (it is published several months after the exam). The answers here are our best-supported answers — derived from careful subject-solving and cross-checked against independent solved papers and primary sources — and will be reconciled to the official key as soon as UPSC publishes it. They are not the official UPSC answer key.

Which one of the following particles in the nucleus of an atom was discovered by J. Chadwick?

(a)Electron
(b)Proton
(c)Positron
(d)Neutron

Answer

Why

Correct — D, Neutron. James Chadwick discovered the neutron in 1932 by bombarding beryllium with alpha particles and detecting a neutral particle of roughly proton mass. The neutron sits in the nucleus alongside the proton and carries no charge, which is why it had eluded earlier experiments.

Why the others are wrong

(a)Electron — The electron was discovered by J. J. Thomson in 1897 through cathode-ray experiments; it orbits the nucleus and is not what Chadwick found.
(b)Proton — The proton was identified by Ernest Rutherford around 1917-19; Chadwick was Rutherford's student but discovered a different, neutral particle.
(c)Positron — The positron, the electron's antiparticle, was discovered by Carl Anderson in 1932 in cosmic rays — it is not a nuclear particle found by Chadwick.

Concept

The nucleus contains protons (positive) and neutrons (neutral). Because the neutron has no charge, it was the hardest nucleon to detect, and its discovery completed the proton-neutron picture of the nucleus.

The distractors are other sub-atomic particles with different discoverers. The safe anchor is the chain 'Chadwick, neutron, 1932'.

Key facts

James Chadwick discovered the neutron in 1932 and won the 1935 Nobel Prize in Physics for it.
The neutron is electrically neutral, with a mass close to that of the proton.
The proton was identified by Rutherford; the electron by Thomson in 1897.
The neutron's discovery made the study of nuclear fission possible.

Portrait of physicist James Chadwick, discoverer of the neutron, seated in a suit at the 1933 Solvay Conference — Chadwick discovered the neutron in 1932, for which he received the 1935 Nobel Prize in Physics.Image: Solvay Conference 1933 (Benjamin Couprie) · Wikimedia Commons (Public domain)

Study next

Discovery of the sub-atomic particles and their discoverersStructure of the atomic nucleus — protons and neutronsIsotopes, mass number and atomic numberNuclear fission and the role of neutronsAtomic models from Thomson to Bohr

Common traps

Attributing the neutron to Rutherford, who found the proton, instead of to Chadwick.
Confusing the positron (Anderson, 1932) with the neutron.

A direct discovery-attribution item — match the scientist to the particle he discovered.

Related PYQs

No directly related past PYQ was found.

Practice

practice — not a real PYQ
The electron was discovered by
- (a)James Chadwick
- (b)J. J. Thomson
- (c)Ernest Rutherford
- (d)Niels Bohr
Answer(b) J. J. Thomson, in 1897.
practice — not a real PYQ
Which sub-atomic particle carries no electric charge?
- (a)Electron
- (b)Proton
- (c)Neutron
- (d)Positron
Answer(c) Neutron.