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

1989

The correct answer is Option (3) → 1989

Sanchi, located in the Raisen district of Madhya Pradesh, was declared a UNESCO World Heritage Site in 1989.

It is renowned for its Greco-Buddhist style and is home to several Buddhist monuments, most notably the Great Stupa, which was originally commissioned by Emperor Ashoka the Great in the 3rd century BCE.