Pure hydrogen sulphide is colourless and has a characteristic

Explanation

Hydrogen sulfide gas has a very distinctive smell exactly like rotten eggs. Even tiny amounts of this gas can be detected by human noses.

The rotten egg smell comes from sulfur compounds breaking down, which is why spoiled eggs smell the same way. Hydrogen sulfide is toxic at high concentrations.

This strong odor serves as a warning sign since the gas is poisonous. Natural gas companies add similar sulfur compounds to help people detect gas leaks.