The correct answer is The red soil colour is caused by aluminium compounds.

• Red Soil: 
  • The red colour of Red Soil is caused by iron compounds. Red soil contains a high percentage of iron content, which is responsible for its colour. 
  • Red soil is a type of soil that develops in a warm, temperate, moist climate under deciduous or mixed forest. Red soils are generally derived from crystalline rock.
• Black Soil:
  • Black soil is called Regur soil and is suitable for cotton cultivation. 
  • It is essentially found in the lava-covered areas of Maharasthra, Karnataka etc. 
• Laterite Soil:
  • Laterite soil is rich in iron oxide and is derived from a wide variety of rocks weathering under strongly oxidizing and leaching conditions.
  • It forms in tropical and subtropical regions where the climate is humid. Lateritic soils may contain clay minerals; but they tend to be silica-poor, for silica is leached out by waters passing through the soil.

• Alluvial Soil:
  • Alluvial soils are soils deposited by surface water. You'll find them along rivers, in floodplains and deltas (like the Mississippi Delta), stream terraces, and areas called alluvial fans. This last category results from larger floods, causing the soil to spread out in the shape of a triangle fan. 
  • Being one of the most important and fertile soils of India they support the growth of a wide variety of crops such as Rice, wheat, sugarcane, cotton, jute, potato and vegetables, but they are deficient in nitrogen, phosphorous and Humus.