Governor Nikhil Kumar will administer the oath of office and secrecy to Rio, who was earlier elected as leader of the Democratic Alliance of Nagaland (DAN) legislature party, and 11 cabinet ministers.
The list of the cabinet ministers is likely to be submitted to the Governor by tomorrow, the sources said.
The Naga People's Front (NPF)-led DAN, having 40 elected members, along with the support of seven Independents, had staked claim to form the government yesterday.