Which of the following Northeastern state was not formed in 1972?

Meghalaya Mizoram Manipur Tripura

Mizoram

Meghalaya was carved out of Assam in 1972. Manipur and Tripura too emerged as separate states in the same year. i.e. 1972. The states of Arunachal Pradesh and Mizoram came into being in 1987.