What mountain ranges flank either side of the central deccan plateau?

The Western and the Eastern Ghats flank either side of the "central Deccan plateau".

Explanation:

The Deccan Plateau was formed by the end of the Cretacious period about "66 million years ago". When the "Indian plate" was moving from above the "Reunion Hotspot", the volcanic eruptions from the hotspot resulted in the formation of the Deccan Plateau. The "western edge" of the "Deccan Plateau" is characterized by the "presence of the Western Ghats" and the eastern edge by the presence of the Eastern Ghats.

The Eastern & Western Ghats flank the Deccan Plateau. They are mountain ranges that are near the coasts of India.