The correct answer is option 1, black soil. Black soil, also known as regur or black cotton soil, is considered to be best suited for cotton cultivation. Black soil is rich in organic matter and has good moisture retention capacity, which is ideal for cotton plants. It also has good drainage properties, preventing waterlogging, which can be detrimental to the cotton crop. Moreover, black soil is fertile and naturally contains essential nutrients required for healthy plant growth. It has a high cation exchange capacity (CEC), which enables it to hold and release nutrients to the plants. Red soil, laterite, and mountain soil are not suitable for cotton cultivation as they lack the necessary characteristics and fertility for cotton plants to thrive.