The correct answer is C. Ammonia.
Ammonia is a colorless gas with a pungent smell. It is produced by the breakdown of urea, which is a waste product of protein metabolism. Ammonia is also found in urine, which is why it is often the cause of the pungent smell near urinals.
Sulphur dioxide is a colorless gas with a suffocating odor. It is produced by the burning of sulfur-containing fuels, such as coal and oil. Sulphur dioxide is also found in volcanic eruptions.
Chlorine is a greenish-yellow gas with a strong, irritating odor. It is used as a disinfectant and bleach. Chlorine is also found in some pesticides.
Urea is a white, crystalline solid with a characteristic odor. It is the main nitrogenous waste product of protein metabolism in mammals. Urea is also found in urine.
In conclusion, the pungent smell often present near the urinals is due to ammonia.