Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: The colloidal surfaces of humus are negatively charged. Reason R: The negative charges arise from exposed functional groups like hydroxyl, carboxylic or phenolic. In the light of the above statements, choose the most appropriate answer from the options given below:

Correct option is A

· Colloidal surfaces of humus: Humus contains colloidal particles that have a negative charge on their surface, which helps in nutrient retention and cation exchange capacity.
· Functional groups: The negative charges arise from functional groups such as hydroxyl (-OH), carboxylic (-COOH), and phenolic (-OH) groups exposed on the surface of humus.
· Explanation: The negative charge of humus colloids attracts positively charged nutrient ions, improving soil fertility.
· Therefore, both Assertion (A) and Reason (R) are true, and R correctly explains A.