Explanation:

- Propine: This is an alkyne, not an aldehyde. Alkynes are hydrocarbons with a triple bond.

- Propanol: This is an alcohol. Alcohols have a hydroxyl group (-OH).

- Propanal: This is an aldehyde. Aldehydes have a carbonyl group (C=O) bonded to at least one hydrogen atom.

- Propanone: Known as acetone, this is a ketone, not an aldehyde. Ketones have a carbonyl group bonded to two carbon atoms.