The southern part of Bihar is rich in minerals and located in the:

Chotanagpur Plateau
Thar Desert
Gangetic Plains
Western Ghats

The correct answer is: Chotanagpur Plateau.

The Chotanagpur Plateau is a plateau in eastern India. It is located in the states of Jharkhand, Bihar, Odisha, and Chhattisgarh. The plateau is rich in minerals, including coal, iron ore, bauxite, and mica.

The Thar Desert is a desert in northwestern India and eastern Pakistan. It is the largest hot desert in India. The desert is located in the states of Rajasthan, Gujarat, and Haryana. The Thar Desert is not rich in minerals.

The Gangetic Plains are a vast plain in northern India. They are located in the states of Uttar Pradesh, Bihar, Jharkhand, West Bengal, and Assam. The Gangetic Plains are the most densely populated region in India. The plains are not rich in minerals.

The Western Ghats are a mountain range in western India. They are located in the states of Maharashtra, Goa, Karnataka, Kerala, and Tamil Nadu. The Western Ghats are a biodiversity hotspot. The mountains are not rich in minerals.