Explanation:

- Option 1: Narmada – It flows westwards through Madhya Pradesh and Gujarat, but is not the longest.

- Option 2: Krishna – This is one of the longest rivers in south India, but shorter than the Godavari.

- Option 3: Godavari – This is the longest river in Peninsular India, often called the "Dakshina Ganga" or "Ganga of the South". Its length is around 1,465 km.

- Option 4: Luni – This flows through Rajasthan, and is much shorter compared to others listed.