Which pair of compounds are classic examples of ptomaines?

• A. Skatole and Indole
• B. Phosphoric acid and Sulfuric acid
• C. Ammonia and Water
• D. Methane and Carbon Dioxide

Answer: (A)

Ptomaines are nitrogen-containing compounds formed by bacteria during the putrefaction of proteins. Indole and skatole are classic examples because they are nitrogenous heterocycles produced from amino acids (tryptophan) during this bacterial breakdown, and they’re well-known for giving the characteristic odors of decomposing matter. Skatole is 3-methylindole, while indole itself is the parent structure, so together they’re the textbook pair cited as ptomaines.

The other choices don’t fit because they’re not nitrogenous bases formed by putrefaction. Mineral acids (phosphoric and sulfuric acids) aren’t ptomaines; ammonia and water aren’t a paired example of this category, and methane with carbon dioxide are simple inorganic or hydrocarbon/inorganic gases, not nitrogenous compounds produced by putrefaction.