The earliest textual reference to the region now known as Assam can be found in:

Mahabharata
Arthashastra
Ramayana
Puranas

The correct answer is: d) Puranas.

The Puranas are a genre of Hindu religious texts that contain a wide range of information, including mythology, history, cosmology, and philosophy. They are believed to have been composed over a period of several centuries, and are considered to be some of the most important texts in Hinduism.

The Puranas contain many references to the region now known as Assam. For example, the Brahmanda Purana states that Assam was once ruled by a king named Narakasura. The Vishnu Purana also mentions Assam, and states that it was once a part of the kingdom of Magadha.

The Puranas are a valuable source of information about the history and culture of Assam. They provide insights into the region’s religious beliefs, social customs, and political history.

The other options are incorrect because:

  • The Mahabharata is an ancient Indian epic poem that does not mention Assam.
  • The Arthashastra is an ancient Indian treatise on statecraft that does not mention Assam.
  • The Ramayana is an ancient Indian epic poem that does not mention Assam.