Which odorant is commonly added to CNG for safety purposes?

The correct answer is the addition of mercaptan to compressed natural gas (CNG) for safety purposes. Mercaptan is a sulfur-containing compound known for its distinctive and strong odor, often compared to the smell of rotten eggs. This characteristic odor is intentionally added to CNG, which is otherwise odorless, to help detect gas leaks. This is crucial for safety as natural gas can be hazardous if it escapes undetected.

The use of mercaptan allows individuals to sense the presence of gas before it reaches dangerous concentrations. Early detection can prevent potential fires, explosions, or other accidents related to gas leaks. This safety measure is a standard practice in the natural gas industry and enhances overall safety for both industrial and residential applications.

Other compounds listed, such as ethanol, aromatic hydrocarbons, and ammonia, do not serve the same purpose when it comes to odorizing natural gas. Ethanol is typically used as a fuel additive rather than an odorant, aromatic hydrocarbons can be present in fuels but do not have the distinct pungency necessary for detecting leaks, and ammonia has a completely different application unrelated to CNG safety. Thus, mercaptan is singularly important for ensuring safe handling and usage of CNG.