Explanations:The Northern Plains of India, also known as the Indo-Gangetic Plain, are primarily composed of alluvial soil. Alluvial soil is a type of soil that is formed by the deposition of sediments by rivers. This process of sediment deposition is a key geological process that shapes the landscape of the Northern Plains.
The Northern Plains are formed by the alluvial deposits of three major river systems: the Indus, the Ganges, and the Brahmaputra. These rivers carry sediments from the Himalayas and deposit them in the plains, creating a fertile layer of soil. The alluvial soil is rich in minerals and organic matter, making it highly suitable for agriculture. This is why the Northern Plains are often referred to as the "breadbasket" of India, as they support intensive farming and are a major source of food production.
It is important to understand the formation of alluvial soil to appreciate the agricultural significance of the Northern Plains. The process of sediment deposition by rivers is continuous, and the soil is replenished regularly, maintaining its fertility. This is in contrast to other soil types, such as black soil, which is found in the Deccan Plateau region and is formed by weathering of basaltic rocks, or alkaline soil, which is found in parts of Rajasthan and Gujarat and is characterized by high pH levels.
Therefore, the correct answer is that the Northern Plains are formed of alluvial soil, which is a result of the geological processes involving river systems and sediment deposition.