What color is the odorant (ethyl mercaptan) added to propane?

The correct answer is that the odorant, ethyl mercaptan, is colorless. Ethyl mercaptan is added to propane as a safety measure because propane in its natural state is odorless and tasteless. Without this odorant, leaks in propane systems could go unnoticed, posing significant safety risks, including the potential for explosions or fires.

In practice, ethyl mercaptan has a very strong, distinctive smell that resembles rotten eggs, which becomes a vital warning signal for detecting gas leaks. The fact that the chemical itself is colorless means that it does not alter the color of the propane, but it serves its purpose due to the strong odor it imparts. The other choices do not apply because while the smell is detectable, the liquid form of ethyl mercaptan is not colored, reinforcing its colorless nature when discussing the substance that is mixed with propane.