At the time of Alexander`s invasion in 326 B.C., the northern part of India was under the rule of the Nanda dynasty, which is Option 1. That`s why it is chosen as the correct answer. Moving to the other options: Option 2, the Maurya dynasty, actually came into power after the decline of the Nanda dynasty and Chandragupta Maurya, the founder of Maurya Empire, is credited with overthrowing the Nandas. As for Option 3, the Sunga dynasty, and Option 4, the Kanva dynasty, both of these came into power much later after the end of the Maurya dynasty. Therefore, none of the options 2, 3, and 4 could be the correct answer.