The question asks for the northernmost river basin of the Deccan Plateau among the given options.

Firstly, let's briefly understand the location of each river and its significance:

• Chambal River: This river is a tributary of the Yamuna River and flows through the Malwa region in central India. It is not part of the Deccan Plateau.
• Mahi River: Originating in Madhya Pradesh, it flows northwards in its initial stage before making a south-westward turn through Rajasthan and Gujarat, eventually draining into the Arabian Sea. It is also located in the western part of India.
• Tapti River: Originating in the Satpura Range of Madhya Pradesh, the Tapti flows westwards across central India before emptying into the Arabian Sea near Surat in Gujarat. Its basin lies entirely within the Deccan Plateau and makes it one of the major rivers draining this region.
• Narmada River: Also rising in the western part of the Deccan Plateau, the Narmada flows west across central India along the Narmada Valley between the Vindhya and Satpura ranges and empties into the Arabian Sea.

Of these rivers, the Tapti River is the northernmost river basin of the Deccan Plateau. It lies close to the Narmada River but is significant as the boundary between the Indian states of Maharashtra and Madhya Pradesh.

Conclusion: The correct option is Tapti, as it has its basin located in the northernmost part of the Deccan Plateau compared to the others listed.