The correct answer is (a) Regur soil.
Regur soil is a type of black soil that is rich in calcium carbonate and magnesium. It is well-drained and has a high water retention capacity, making it ideal for cotton cultivation. Cotton is a thirsty crop that requires a lot of water, and regur soil is able to provide this. Additionally, regur soil is rich in nutrients that are essential for cotton growth, such as nitrogen, phosphorus, and potassium.
Laterite soil is a type of red soil that is formed in tropical and subtropical regions. It is low in nutrients and has a high acidity, making it unsuitable for cotton cultivation. Alluvial soil is a type of soil that is formed from the deposition of sediments by rivers. It is rich in nutrients and has a good drainage system, making it suitable for a variety of crops, including cotton. Red soil is a type of soil that is formed from the weathering of rocks. It is low in nutrients and has a high acidity, making it unsuitable for cotton cultivation.
In conclusion, regur soil is the most suitable soil for cotton cultivation in India. It is rich in nutrients, has a good drainage system, and is able to provide the water that cotton requires.