Arunachal Pradesh was granted statehood in:

The correct answer is Option (4) → 1987

Arunachal Pradesh became a full state on 20 February 1987, under the State of Arunachal Pradesh Act, 1986. The area was earlier the North-East Frontier Agency (NEFA); it was made a Union Territory named Arunachal Pradesh in 1972 and was raised to statehood fifteen years later.