The correct answer is: c) Khawthlangtuipui (Karnaphuli)
The Khawthlangtuipui (Karnaphuli) is the longest river flowing entirely within Mizoram. It is a tributary of the Feni River, which flows into the Bay of Bengal. The Khawthlangtuipui is about 200 kilometers long and originates in the Lushai Hills. It flows through the states of Mizoram and Tripura before joining the Feni River. The river is a major source of water for irrigation and drinking water in Mizoram. It is also a popular tourist destination, with many people visiting the river to go swimming, fishing, and boating.
The other options are incorrect because they are not rivers that flow entirely within Mizoram. The Tlawng is a river that flows through the states of Mizoram and Assam. The Tuivai is a river that flows through the state of Mizoram. The Kolodyne (Chhimtuipui) is a river that flows through the states of Mizoram and Tripura.