Answer: B. Ukraine
Explanation: The Chernobyl nuclear disaster occurred on April 26, 1986, at the nuclear power plant Chernobyl. Chernobyl power plant is located near the Pripyat city of Ukraine, which was then a part of the Soviet Union. The fire that arose as a consequence of this nuclear disaster was localized on May 4, 1986. The effects of this accident were fatalities immediately after the explosion of the deadly vapour in the air, as well as subsequent deaths from the consequence of an excessive radiation dose.