Exp) Option b is the correct answer.

Pair I is correct: The capital of Arunachal Pradesh is Itanagar, located in the Papumpare district. The city derives its name from the historic Ita Fort, meaning “Fort of Bricks,” which was built in the 14th century AD. Arunachal Pradesh finds mention in ancient Indian texts such as the Kalika Purana and the Mahabharata, where it is referred to as the Prabhu Mountains in the Puranas.

Pair II is correct: Nagaland was given statehood in 1963 through the State of Nagaland Act, 1962.  In July, 1960, an agreement was reached by the Government of India with the leaders of the Naga Peoples Convention under which it was decided that Naga Hills-Tuensang Area (Nagaland), which is at present a Part ‘B’ tribal area within the State of Assam, will be formed into a separate State in the Union of India. Thus, two motions were introduced together i.e. motions regarding the Constitution (Thirteenth Amendment) Bill, 1962, and the State of Nagaland Bill, 1962. 13th Constitutional amendment Act was introduced to amend Article 371 and insertion of Artice 371 A. While State of Nagaland bill passage led to the formation of state of Nagaland.

Pair III is correct:  Based on the four-fold classification of the states and territories of the Indian Union in Indian Constitution in 1950,  Tripura was categorised as Part C state, and later became the Union territory based on State Reorganisation Act of 1956 and finally became the 20th state of India in 1972

Source: https://arunachalgovernor.gov.in/html/history.htm#:~:text=Capital%20of%20the%20State%20is,the%20Prabhu%20Mountains%20of%20Puranas.

Laxmikant- Indian Polity- Appendix IV Constitutional Amendments at a Glance

Laxmikant- Indian Polity -EVOLUTION OF STATES AND UNION TERRITORIES