A major coastal plain in Tamil Nadu is the:

Malabar Plain
Coromandel Plain
Konkan Plain
Deccan Plateau

The correct answer is (b). The Coromandel Plain is a major coastal plain in Tamil Nadu. It is located on the eastern coast of India, and is bordered by the Bay of Bengal to the east and the Western Ghats to the west. The Coromandel Plain is a fertile region, and is home to a number of important cities, including Chennai, Madurai, and Coimbatore.

The Malabar Plain is located on the western coast of India, and is bordered by the Arabian Sea to the west and the Western Ghats to the east. The Malabar Plain is a hilly region, and is home to a number of important cities, including Kochi, Thiruvananthapuram, and Kozhikode.

The Konkan Plain is located on the western coast of India, and is bordered by the Arabian Sea to the west and the Western Ghats to the east. The Konkan Plain is a narrow coastal plain, and is home to a number of important cities, including Mumbai, Pune, and Goa.

The Deccan Plateau is a large plateau located in the central and southern parts of India. It is bordered by the Himalayas to the north, the Western Ghats to the west, the Eastern Ghats to the east, and the Bay of Bengal to the south. The Deccan Plateau is a dry and arid region, and is home to a number of important cities, including Hyderabad, Bangalore, and Pune.