The correct answer is: A. Found in upper Ganga plain
Khadar soil is a type of alluvial soil found in the upper Ganga plain. It is a relatively young soil, having been formed in the last few thousand years. Khadar soil is rich in nutrients and is well-drained. It is ideal for growing rice, wheat, and other crops.
Option B is incorrect because Khadar soil is not rich in nitrogen. In fact, it is relatively low in nitrogen. This is because Khadar soil is formed from the deposition of silt and clay by the Ganges River. These sediments are low in nitrogen.
Option C is incorrect because Khadar soil does not have a higher Kankar concentration than other types of soil. Kankar is a type of calcium carbonate concretion that forms in soils with high calcium levels. Khadar soil does not have high calcium levels, so it does not form Kankar.
Option D is incorrect because Khadar soil is a type of alluvial soil. Alluvial soils are formed from the deposition of sediments by rivers. Khadar soil is a type of alluvial soil that is found in the upper Ganga plain.