Option 1: Tapti River -> Flows westward and drains into the Arabian Sea.
Option 2: Mandovi River -> Flows westward and drains into the Arabian Sea.
Option 3: Mahanadi River -> Flows eastward and drains into the Bay of Bengal.
Option 4: Narmada River -> Flows westward and drains into the Arabian Sea.
Hence, Option 3: Mahanadi River -> It is the only river among the given options that flows eastward into the Bay of Bengal, while all others (Tapti, Mandovi, and Narmada) are west-flowing rivers that drain into the Arabian Sea -> correct