The correct answer is option 3, Anguttara Nikaya. The Anguttara Nikaya is one of the five collections of the Sutta Pitaka, which is a division of the Buddhist scriptures known as the Tripitaka. The Anguttara Nikaya contains discourses given by the Buddha that are organized according to numerical patterns. Each discourse in this collection focuses on a specific number, such as one, two, three, etc. It is in the Anguttara Nikaya that the 16 Mahajana-padas are described. The term "Mahajana-pada" refers to the sixteen great kingdoms or republics of ancient India during the time of the Buddha. These kingdoms were important political entities and the Buddha often used them as examples in his teachings.