Explanation:

- Son (Option 1): The Son River is a major southern tributary of the Ganga. It flows through central India and joins the Ganga near Patna.

- Ramganga (Option 2): The Ramganga River is a significant northern tributary of the Ganga. It enters the Ganga near Kannauj in Uttar Pradesh.

- Kali (Option 3): There are a few rivers with similar names, such as the Kali River in Uttarakhand, but they are part of the Ganga's tributary system, making them indirectly connected to the Ganga.

- Penganga (Option 4): The Penganga is not a tributary of the Ganga. It is part of the Godavari River basin in southern India.

The correct answer is:

- Penganga (Option 4)