Answer : 3. "21 मई "
Explanation :

National Anti-Terrorism Day is celebrated across the country every year on 21 May. On this day in 1991, former Prime Minister Rajiv Gandhi was assassinated in a suicide bomb blast. This day is celebrated to tackle global threats and raise awareness about the importance of unity. Rajiv Gandhi took over as Prime Minister after the assassination of his mother Indira Gandhi on October 31, 1984 and held this post from 1984 to 1989.