Aspergillus niger is used to test the status of which element in the soil

Answer: Option C

Aspergillus niger is used to test the status of potassium elements in the soil. It is used as a test organism for determining Mg, Cu, Zn, Mo, etc in soil.
Aspergillus niger is a haploid filamentous fungus that is used for waste management and biotransformation in addition to its industrial uses, such as the production of citric acid and extracellular enzymes.