Olsen's method, which is used for phosphorus detection method used in soil is

Answer: Option A

The Olsen method is a chemical extractant (bicarbonate) that provides a reasonable estimate of the amount of plant-available P by measuring phosphate from the soil solution and exchange surfaces.
This procedure is suitable for all expected sodic soils, calcareous, alkaline, neutral and slightly acidic soils containing CaPO₄, since the calcium concentration in the solution is suppressed by the precipitation of CaCO₃, increasing PO₄ concentration in the solution.