Assertion: After independence, there was a demand for autonomy in Assam.
Reason: The state wanted to secede from India but was unable to.

The Assertion is correct but the Reason is incorrect.

At independence the entire region except Manipur and Tripura comprised the State of Assam. Demands for political autonomy arose when the non-Assamese felt that the Assam government was imposing Assamese language on them. There were opposition and protest riots throughout the State. Leaders of the major tribal communities wanted to separate from Assam. They formed the Eastern India Tribal Union which later transformed into a more comprehensive All Party Hill Leaders Conference in 1960. They demanded a tribal State to be carved out of Assam Finally instead of one tribal State, several States got carved out of Assam. At different points of time the Central Government had to create Meghalaya, Mizoram and Arunachal Pradesh out of Assam. Tripura and Manipur were upgraded into States too.