India’s first atomic reactor was

Apsara
Kamini
Zerlina
Dhruva

India’s first atomic reactor was Apsara. It was a natural uranium-fueled, heavy water moderated reactor that went critical on August 4, 1956. Apsara was built at the Bhabha Atomic Research Centre (BARC) in Trombay, Mumbai. It was used for research and training purposes.

Kamini was a plutonium-fueled, heavy water moderated reactor that went critical on December 10, 1954. It was also built at BARC. Kamini was used for research and production of plutonium for India’s nuclear weapons program.

Zerlina was a research reactor that was built at BARC in 1960. It was a small, low-power reactor that was used for research on nuclear fuel materials and reactor physics.

Dhruva was a research reactor that was built at BARC in 1985. It is a larger and more powerful reactor than Apsara or Kamini. Dhruva is used for research on nuclear fuel materials, reactor physics, and materials science.

In conclusion, India’s first atomic reactor was Apsara. It was a natural uranium-fueled, heavy water moderated reactor that went critical on August 4, 1956. Apsara was built at the Bhabha Atomic Research Centre (BARC) in Trombay, Mumbai. It was used for research and training purposes.