Question

This question consists of two statements, Assertion and Reason. While answering this question you are required to choose any one of the following five responses.

Assertion: Main constituent of human urine is ammonia.

Reason: If human urine is allowed to stand for some time, it smells strongly of ammonia.

Answer 1

Assertion-Reason relation

Humans are ureotelic animals, that means they excrete the nitrogenous wastes in the form of urea. Ammonia produced as a metabolic waste is highly toxic, hence, gets converted to urea before excretion through urine.
Major portion of urine is composed of water. The rest portion consists of urea, dissolved ions and other wastes.
Hence, the assertion statement is incorrect.

Human urine when is allowed to stand for some time, the urea in it gets decomposed to form ammonia. Hence, it smells strongly of ammonia. So, the reason statement is correct.