For determination of soil microbial biomass, carbon extracting agent used is

Correct option is A

✅ (a) Potassium sulphate [K₂SO₄] • 0.5 M K₂SO₄ is commonly used for extracting microbial biomass C from soil. • It helps to solubilize microbial cell contents after fumigation. • Provides consistent results in chloroform fumigation-extraction method. • Does not interfere with carbon measurements.
❌ (b) Ammonium sulphate • Not suitable for C extraction; more relevant for N analysis. • May react differently with organic carbon in soil.
❌ (c) Silver sulphate • Primarily used in COD analysis. • Not standard for microbial biomass estimation.
❌ (d) Sodium sulphate • Lacks the extraction efficiency of K₂SO₄. • Not recommended in established protocols.