Option a is the correct answer. Option 1 is incorrect: Arthashastra was a detailed treatise on administration written by Chanakya. It contains details about the administrative system, political system, defence strategies and economic policies of the Mauryan Empire under Chandragupta's reign. It does not mention about 16 Mahajanpads. Option 2 is correct: Anguttara Nikaya describes 16 Mahajanapadas. It is a Buddhist scripture, which is the fourth of the five Nikayas or collections in the Sutta Pitaka. Option 3 is incorrect: Buddhist text the Digha Nikaya mentions 12 Mahajanapadas (not 16 Mahajanapadas) and four of them which are not part of this book were Assaka, Avanti, Gandhara, and Kamboja. Option 4 is correct: The Bhagwati Sutra is a Jain text that describes the life and teachings of Mahavira, the 24th Tirthankara of Jainism. It also describes the 16 Mahajanapadas, which were the 16 most powerful and prosperous kingdoms in ancient India. However, the Mahajanpads given in this text is slightly different from the 16 Mahajanpads given in the Anguttara Nikaya.