The basis of soil testing, the critical limit for 'Sulphur' in soil is:

Correct option is B

In soil testing, the critical limit refers to the soil nutrient concentration below which crops are likely to respond to fertilizer application and above which a response is unlikely.

For available sulphur (S) in soil:

Extensive field calibration studies conducted by ICAR and State Agricultural Universities have established 10 ppm (10 mg/kg) as the generalized critical limit.

Soils containing < 10 ppm sulphur are considered deficient and show crop response to sulphur fertilization.

Soils with ≥ 10 ppm sulphur are considered sufficient.

Therefore:

05 ppm → too low and not an accepted critical limit

10 ppm → standard and correct

15 ppm & 20 ppm → well above the critical limit