Question

The urine on standing gives a pungent smell in public urinals generally, is due to
A. Conversion of urea into ammonia by bacteria
B. Conversion of both urea and uric acid into ammonia
C. Conversion of uric acid into ammonia by ornithine cycle
D. None of the above

Answer 1

Urine is the result of filtration, reabsorption, and tubular secretion which takes place in kidneys.
Urine contains various waste products such as urea, inorganic salts, creatinine, and other waste products from the bloodstream along with excess water which is not required by our body.

Complete answer:
Humans are ureotelic, which means it excretes urea.
Urea is also known as carbamide. The chemical formula of urea is CO${({NH_2})_2}$ where amide has two -${NH_2}$ groups that are joined by a carbonyl (C=O) functional group.
Urea is odorless and non-toxic.
When urine stands for a long time in a public urinal the bacteria accumulate in the urine and converts the urea into ammonia by enzyme urease present in bacteria. The bacteria break down urea into ammonia and carbon dioxide.
Ammonia has a pungent smell which makes the urinal full of pungent odor.

So, the answer is A. Conversion of urea into ammonia by bacteria.

Note: Some soil- bacteria convert urea into ammonia which helps the farmer as a fertilizer. In agriculture, nitrogen-containing compounds are continuously used to facilitate the growth of plants and to maximize crop yielding.
Along with bacteria some fungi also contain the enzyme urease, which helps in the breakdown of urea to ammonia.
Ammonia can raise the pH of cells to a toxic level. It is a volatile compound.