The correct answer is: a) Shillong Accord.
The Shillong Accord was signed on 21st April 1975 between the Government of India and the All Party Hill Leaders Conference (APHLC) to resolve the political crisis in the hill districts of Assam. The accord paved the way for the creation of an autonomous district council within Assam for the hill districts that later became Meghalaya.
The Guwahati Accord was signed on 15th August 1985 between the Government of India and the National Socialist Council of Nagaland (Isak-Muivah) (NSCN-IM) to resolve the Naga political conflict. The accord led to the creation of a new state of Nagaland within the Indian Union.
The Mizo Peace Accord was signed on 30th June 1986 between the Government of India and the Mizo National Front (MNF) to resolve the Mizo National Front insurgency. The accord led to the creation of a new state of Mizoram within the Indian Union.
The Tashkent Agreement was signed on 10th January 1966 between India and Pakistan to end the Indo-Pakistani War of 1965. The agreement did not address the issue of Kashmir.