The correct answer is: A. North Bihar plain
Lime concentration is higher in the North Bihar plain because of the presence of limestone deposits in the area. Limestone is a type of sedimentary rock that is composed of calcium carbonate. When limestone is weathered, it releases calcium carbonate into the soil. Calcium carbonate is a base, and it can raise the pH of the soil. A higher pH can make the soil more alkaline, which can be beneficial for some plants.
The South Bihar plain is also a sedimentary plain, but it does not have as much limestone as the North Bihar plain. As a result, the lime concentration in the South Bihar plain is lower than in the North Bihar plain.
The North-West Bihar plain is a hilly region, and it does not have as much limestone as the North Bihar plain. As a result, the lime concentration in the North-West Bihar plain is lower than in the North Bihar plain.
The South-East Bihar plain is a coastal region, and it does not have as much limestone as the North Bihar plain. As a result, the lime concentration in the South-East Bihar plain is lower than in the North Bihar plain.