Explanation:

The Chernobyl tragedy was the result of a nuclear accident on 26 April 1986 at reactor No. 4 at the Chernobyl Nuclear Power Plant, near the town of Pripyat in the Ukrainian SSR (Ukrainian Soviet Socialist Republic).

• There were nearly 8.4 million people exposed to radiation in the three nations.
• It occurred when a group of technicians in what was then Soviet-controlled Ukraine carried out a botched safety test that led to a series of explosions.
• It is said to have released 400 times more radiation than the atomic bomb that was dropped on Hiroshima in Japan.

Hence option 1st is correct.