The black cotton soil of India has been formed due to the weathering of

The correct option is Fissure volcanic rock.

Black cotton soil, also known as Regur soil, is widely found in the Deccan Trap region of India, covering parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, and Tamil Nadu.

Formation Process:
During the Cretaceous period, massive volcanic eruptions occurred along long cracks or fissures in the Earth's crust (fissure eruptions). Dense, basic basaltic lava overflowed and cooled over large areas, forming basaltic volcanic rocks.

Over millions of years, the continuous weathering and erosion of these fissure volcanic rocks under specific climatic conditions broke them down into fine clayey particles, resulting in the formation of rich black cotton soil.

Key Characteristics of Black Cotton Soil:
1. Rich in minerals like iron, lime, calcium, potassium, aluminum, and magnesium.
2. High water-retaining capacity.
3. Develops deep cracks during dry seasons, which helps in self-aeration.
4. Exceptionally suitable for growing cotton crops.