India is an important member of the ‘International Thermonuclear Experimental Reactor’. If this experiment succeeds, what is the immediate advantage for India?

The correct answer is D. ITER is a fusion project, not a fission one. It aims to show that the fusion of deuterium and tritium can produce far more energy than it takes in, with a target of about ten times the input. If that works, the next step is commercial fusion power plants, and that is the advantage India gains as a partner.

• A is wrong. Thorium is a fertile material used in fission breeder cycles. Fusion does not use thorium, and ITER has nothing to do with thorium-based power.
• B is wrong. Satellite navigation is a separate domain. India's own system is NavIC (IRNSS), and ITER has no connection to it.
• C is wrong. Fusion and fission are different processes. A success at ITER does not improve the efficiency of existing fission reactors.

The core concept is the difference between fission (splitting heavy nuclei, as in today's reactors) and fusion (joining light nuclei, as in the Sun). For the Mains, this links to India's three-stage nuclear programme under Homi Bhabha and to long-term energy security and decarbonisation. Note that ITER's timelines have been revised several times, so the benefit is still prospective.

Trap: Aspirants who know India's thorium reserves often pick A by reflex, mixing up fusion with the thorium fission cycle.