Option 1: All Mahajanapadas were oligarchies where power was exercised by a group of people. This statement is not correct. The power structure of the Mahajanapadas varied. Some were ruled by kings while others had a republican form of government. Therefore, it cannot be said that all Mahajanapadas were oligarchies.

Option 2: All Mahajanapadas were located in eastern India. This statement is not correct. The Mahajanapadas were located in various parts of ancient India, including both the northern and eastern regions. Some of the prominent Mahajanapadas were located in present-day Bihar, Bengal, Uttar Pradesh, and Madhya Pradesh.

Option 3: No army was maintained by the Mahajanapadas. This statement is not correct. The Mahajanapadas were known for their military strength. They maintained powerful armies to protect their territories and engage in warfare with neighboring states. The armed forces of the Mahajanapadas consisted of infantry, cavalry, and elephants.

Option 4: Buddhist and Jaina texts list sixteen Mahajanapadas. This statement is correct. According to Buddhist and Jaina texts, there were sixteen Mahajanapadas in ancient India. These texts mention the names of these sixteen Mahajan