The correct answer is: c) Interior districts.
Red soils are commonly found in the interior districts of Tamil Nadu. These soils are formed from the weathering of granite and gneiss rocks. They are rich in iron and aluminum oxides, which give them their characteristic red color. Red soils are well-drained and have good water retention capacity. They are suitable for growing a variety of crops, including rice, sugarcane, and cotton.
Coastal plains are covered by alluvial soils, which are formed from the deposition of sediments by rivers. These soils are rich in nutrients and are suitable for growing a variety of crops, including rice, sugarcane, and coconut.
River deltas are formed at the mouth of a river, where the river meets the sea. The sediments deposited by the river form a fan-shaped delta. The soils in river deltas are rich in nutrients and are suitable for growing a variety of crops, including rice, sugarcane, and coconut.
Mountainous regions are covered by a variety of soils, depending on the type of rock that is being weathered. The soils in mountainous regions are generally not as fertile as the soils in other parts of the state. However, they are suitable for growing a variety of crops, including tea, coffee, and spices.