Explanation:

• The Brus, also referred to as the Reangs, are spread across the north-eastern states of Tripura, Assam, Manipur, and Mizoram. However, they are recognised as a Particularly Vulnerable Tribal Group (PVTG) only in Tripura.
• In 1973, the Dhebar Commission created Primitive Tribal Groups (PTGs) as a separate category, that are less developed among the tribal groups.
• In 2006, the Government of India renamed the PTGs as Particularly Vulnerable Tribal Groups (PVTGs).
• There are 75 PVTGs.  The criteria followed for determination of PVTGs are: A pre-agriculture level of technology; A stagnant or declining population; Extremely low literacy; and A subsistence level of economy.

Hence only option 2nd is correct.