ANS:D - pungent smell of mercaptans present in the gas.

Mercaptans, also known as thiol compounds, are organic sulfur-containing compounds characterized by their pungent and unpleasant odor resembling that of rotten eggs or skunk spray. These compounds are commonly added to odorless gases, such as natural gas or liquefied petroleum gas (LPG), for safety reasons. The pungent smell of mercaptans is used as a safety measure to detect gas leaks. When added to odorless gases, even in very small concentrations, mercaptans impart a strong and distinctive odor that is easily detectable by humans at low levels. This odor serves as a warning sign, alerting individuals to the presence of gas leaks before they can pose a serious risk. In the context of a cooking gas cylinder, the presence of mercaptans allows individuals to detect gas leaks by simply smelling the air around the cylinder. If there is a leak, the characteristic odor of mercaptans will be noticeable, indicating the presence of gas escaping from the cylinder. This provides an early warning, allowing individuals to take appropriate actions such as shutting off the gas supply, ventilating the area, and contacting emergency services if necessary. Overall, the pungent smell of mercaptans is an important safety feature implemented in gas cylinders and other gas distribution systems to help detect leaks and prevent potential accidents or hazards associated with the buildup of flammable or toxic gases.