The Correct answer is option 'D' i.e. 1991.

Explanation:
A coup took place in the Soviet Union on August 19-21, 1991, which was a failed attempt by a group of hardline Communist Party officials to overthrow Soviet leader Mikhail Gorbachev and seize control of the Soviet Union. The coup was launched by a group of eight high-ranking Soviet officials who were known as the State Committee on the State of Emergency, or the "Gang of Eight".

The coup leaders were unhappy with Gorbachev's reforms, which they believed were undermining the Soviet system. They also wanted to prevent the signing of a new union treaty that would have given greater autonomy to the Soviet republics.

The coup began on August 19, 1991, when the Gang of Eight placed Gorbachev under house arrest while he was on vacation in the Crimea. They then declared a state of emergency, suspended the Soviet constitution, and took control of the media.

However, the coup leaders were unable to gain the support of the military or the people, and their attempt to seize power quickly collapsed. Demonstrators took to the streets in Moscow and other cities, and the military refused to obey the coup leaders' orders.

By August 21, Gorbachev had been released from house arrest, and the coup leaders had fled Moscow. The coup's failure marked the end of the Soviet Union and paved the way for the establishment of the Russian Federation.

In conclusion, the Soviet coup took place in 1991.