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

1. A

   It can use thorium in place of uranium for power generation

   Using thorium in place of uranium is the long-term aim of India’s three-stage nuclear power programme (PHWR–FBR–thorium), not the immediate payoff of ITER. ITER is a fusion experiment with deuterium–tritium fuel, not a thorium fission route. This option is not the key.

2. B

   It attains a global role in satellite-navigation

   A global role in satellite navigation is IRNSS/NavIC, unrelated to ITER. This option is wrong.

3. C

   It can drastically improve the efficiency of its fission reactors in power generation

   Improving the efficiency of fission reactors is reactor-engineering and fuel-cycle work at home. ITER does not upgrade India’s PHWRs. This option is not the key.

4. D

   It can build fusion reactors for power generation

   ITER is an international tokamak to demonstrate the scientific and technological feasibility of fusion power. If it succeeds, participating countries, including India, gain the knowledge base to build fusion reactors for electricity. That immediate strategic advantage is why (d) is the official key.

Summary. Official key is (d) it can build fusion reactors for power generation. ITER (Cadarache, France) is not a commercial plant; it is the experimental step before DEMO-class fusion reactors. India’s three-stage thorium programme is fission and is separate. Navigation satellites and PHWR efficiency are different science programmes. Success at ITER would still be fusion, not thorium fission.