The correct answer is: a) Sadiya.
Sadiya is a town in the Tinsukia district of Assam, India. It is located on the banks of the Brahmaputra River, about 300 kilometers (190 mi) east of Guwahati. Sadiya was the capital of the Chutiya kingdom from the 13th to the 16th centuries. The Chutiyas were a Tibeto-Burman people who ruled over a large area of what is now Assam and Arunachal Pradesh. The capital of the Chutiya kingdom was located at Sadiya because it was a strategic location on the Brahmaputra River. The Chutiyas were able to control trade and travel along the river from their capital at Sadiya.
The other options are incorrect because they are not located in Assam. Itanagar is the capital of Arunachal Pradesh, Tawang is a town in Arunachal Pradesh, and Bomdila is a town in Arunachal Pradesh.