In an experiment to determine the percentage of humus content in a soil, the following results were obtained:
mass of dish = 10 gm
mass of dish and oven-dry soil = 50 gm
mass of dish and soil after heating = 40 gm
Calculate the percentage of humus in the soil sample.

• A.10 %
• B.25%
• C.60%
• D.75%
• E.80%