Detailed Explanation:

Answer: Option 2 — fissure volcanic rock

Black cotton soil (also known as Regur soil) in India is primarily formed by the weathering of basaltic lava flows from fissure volcanic eruptions. These soils are predominantly found in the Deccan Plateau region, covering parts of Maharashtra, Gujarat, Madhya Pradesh, and Karnataka, where the parent material is basaltic rock. The dark color comes from the presence of titaniferous magnetite and aluminum-rich minerals, while the high clay content gives it swelling and shrinking properties.

📝 Short Notes: Black Cotton Soil (Regur Soil)

• Parent Material: Formed from weathering of basaltic lava (Deccan Trap volcanic rocks)
• Geographical Distribution: Deccan Plateau, Malwa Plateau - mainly in Maharashtra, Gujarat, Madhya Pradesh, Karnataka, parts of Andhra Pradesh and Tamil Nadu
• Physical Properties: Deep black to dark gray color; rich in clay, lime, iron, magnesium, and aluminum but deficient in nitrogen, phosphorus, and organic matter
• Characteristic Feature: High clay content causes swelling when wet and shrinking when dry, developing deep cracks in summer
• Moisture Retention: Excellent moisture retention capacity due to high clay content, suitable for dry farming
• Major Crops: Ideal for cotton cultivation; also suitable for sugarcane, jowar, wheat, linseed, and citrus fruits
• Other Names: Regur soil, Black soil, or Tropical Black Earth