Explanation:

- Option 1: Dhruva

- India's largest research reactor.

- Commissioned in 1985 at Bhabha Atomic Research Centre (BARC), Mumbai.

- Mainly used for producing radioisotopes and neutron activation analysis.

- Option 2: Apsara

- The first nuclear research reactor in Asia.

- Commissioned in 1956, also located at BARC.

- Primarily used for isotope production and research.

- Option 3: Circus

- No known reactor by this name in India.

- Possibly a misinterpretation or error.

- Option 4: Kamini

- A unique research reactor operating with uranium-233 fuel.

- Located at the Indira Gandhi Centre for Atomic Research in Kalpakkam.

- Mainly used for research and isotope production.