Correct Option (A)
The Nanda dynasty was ruling over Magadha in North India at the time of Alexander's invasion of India (326 BCE). The last ruler of the Nanda dynasty was Dhana Nanda, who was known for his vast army and immense wealth. Alexander's forces, having heard of the formidable Nanda army, mutinied and refused to advance further into India, leading to Alexander's eventual retreat.
Incorrect Options:
The Maurya dynasty was established by Chandragupta Maurya after overthrowing the Nanda dynasty, subsequent to Alexander's departure from India. Therefore, the Mauryas were not in power during Alexander's invasion.
The Sunga dynasty succeeded the Mauryas, founded by Pushyamitra Sunga after assassinating the last Mauryan emperor, Brihadratha. This occurred much later than Alexander's invasion.
The Kanva dynasty followed the Sunga dynasty, established by Vasudeva Kanva. This dynasty also emerged significantly after Alexander's invasion of India.