In which year was Sanchi declared as a World Heritage Site?

The correct answer is Option (3) → 1989

The Buddhist Monuments at Sanchi, in the Raisen district of Madhya Pradesh, were inscribed on UNESCO’s World Heritage List in 1989. The group is centred on the Great Stupa, begun by the Mauryan emperor Ashoka in the 3rd century BCE and enlarged later, with its four carved gateways (toranas).