Explanation:

Sikkim(22nd state) was made a full-fledged state under 36th Constitutional Amendment Act (1975).
The Union Territory of Mizoram was conferred the status of a full state as a sequel to the signing of a memorandum of settlement (Mizoram Peace Accord) in 1986 between the Central government and the Mizo National Front, ending the two-decade-old insurgency.
Arunachal Pradesh was made a state by the State of Arunachal Pradesh Act, 1986, with effect from February 20, 1987.
In 1987, Goa was made a 25th state of India by the Goa, Daman and Diu Reorganisation Act, 1987.