On what basis is the best distinction between Khadar and Bhangar in the Northern Plains made?

Correct answer: New and old alluvial deposits

The direct answer is A: new and old alluvial deposits. Alluvium is material such as sand, silt, clay, and gravel deposited by rivers. Khadar is the newer alluvium found close to active river channels or floodplains. It may be renewed during floods and is generally finer and more fertile. Bhangar is the older alluvium lying on slightly higher terraces beyond the usual flood area. It is more compact and may contain kankar, or calcium-carbonate nodules. Therefore the most accurate basis of distinction is the age and position of the alluvial deposit. Option A is correct. Option B, red and black soil, is a colour-based soil comparison and does not define Khadar and Bhangar. Option C, eastern and western coast, compares coastal regions and has no relation to these northern plain deposits. Option D, river and mountain height, does not classify alluvium; both terms are associated with river-made plains, not mountain elevation. A useful exam caution is that Khadar is generally more fertile because fresh silt is added, but the basic defining difference is new versus old alluvium.