The known forces of natures can be divided into four classes, viz., gravity, electromagnetism, week nuclear force and strong nuclear force. With reference to them, which one of the following statements is not correct?

The correct answer is A. Gravity is the weakest of the four fundamental forces, not the strongest. The strength order is strong nuclear, then electromagnetic, then weak nuclear, then gravity. Between two protons, gravity is roughly 10^36 times weaker than electromagnetic repulsion, which is why gravity matters only when masses are very large, as with planets and stars.

Why the other options are correct:

• B: Electromagnetism acts only on particles with electric charge. Photons and neutrinos, having no charge, do not feel it.
• C: The weak nuclear force governs beta decay, where a neutron changes into a proton, electron and antineutrino. This is the mechanism behind much natural radioactivity.
• D: The strong nuclear force binds quarks into protons and neutrons, and its residual effect holds nucleons together against the electrostatic repulsion between protons.

Core concept: the four fundamental interactions, their relative strengths and their ranges. Mains angle: the Standard Model and the search for unification, linked to the 2012 Higgs discovery and the frontiers of science and technology under GS-III.

Trap: Aspirants often assume gravity is the strongest force because we feel it every day. Felt strength and intrinsic strength are different things.