What substance is commonly added to natural gas to give it an odor?

The substance commonly added to natural gas to give it an odor is mercaptan. Natural gas is odorless when it is extracted, which makes it difficult to detect in case of a leak. Mercaptan has a distinct, strong smell often compared to rotten eggs, which serves as a safety measure to alert individuals to the presence of gas. This warning system is critical for preventing potential hazards associated with gas leaks, allowing people to take appropriate action if they smell gas.

The other choices are not used for this purpose. Propane and butane are hydrocarbons that can be used as fuels themselves, but they do not serve as odorants for natural gas. Ethanol is an alcohol commonly used as a fuel additive and does not provide the characteristic odor needed for safety in gas detection. Overall, mercaptan is the standard additive due to its effectiveness in odorizing natural gas and enhancing safety protocols in gas usage.