Which reactor at BARC used Plutonium Oxide as fuel and in which year was it established?

The correct answer is Option C — Purnima-1 (1972). Purnima-1 (Plutonium Reactor for Neutron Investigation in Multiplying Assemblies) was established in 1972 at BARC Mumbai. It was the first fast neutron research reactor in India and used plutonium oxide as fuel and light water as moderator. It achieved criticality on May 18, 1972. Option A is incorrect: Apsara (1956) used enriched uranium as fuel and light water as moderator. It was India's first reactor not Purnima-1. Option B is incorrect: CIRUS (1960) used natural uranium as fuel and heavy water as moderator. It was Canada-assisted reactor. Option D is incorrect: Dhruva (1985) uses natural uranium as fuel and heavy water as moderator. It is India's largest indigenous research reactor with 100 MW thermal power. Purnima-1 was shut down and upgraded to Purnima-2 in 1984 which used Uranium-233 as fuel.