They are highly eroded and broken hills.
Explanation
The Aravali Hills are one of the oldest geological features on Earth. They are classified as Old Fold Mountains that originated during the Precambrian era. Over millions of years, they have been subjected to intense denudation, transforming them into residual or relict mountains.
Option-wise Analysis
- They are young fold mountains. is Incorrect: The Aravalis are Old Fold Mountains, not young fold mountains. Young fold mountains, such as the Himalayas, were formed much later during the Tertiary period.
- They are highly eroded and broken hills. is Correct: Due to their immense age and continuous exposure to weathering agents, the Aravalis have been significantly worn down. They now exist as highly eroded and broken hills (relict mountains).
- They lie on the eastern margins of the Peninsular plateau. is Incorrect: The Aravali Hills lie on the western and northwestern margins of the Peninsular Plateau, not the eastern margins. The eastern margins are marked by the Eastern Ghats and the Rajmahal Hills.
- They extend from Delhi to Gujarat in a northwest-southeast direction. is Incorrect: The range extends from Gujarat to Delhi in a Southwest-Northeast direction. The option incorrectly states the direction as northwest-southeast.
Key Takeaway: The Aravali Range is the oldest fold mountain system in India, located on the northwestern margin of the Peninsular Plateau, extending in a SW-NE direction as highly eroded relict hills.