Two carbon compounds have the prefix eth-, the prefix pro- applies to three carbon atoms.
Propane: CH₃CH₂CH₃, alkane molecule, completely saturated and contains no double bonds
Propene: CH₃CH=CH₂, alkene molecule, single degree of unsaturation and contains one double bond
Propyne: CH₃C≡CH, alkyne molecule, two degrees of unsaturation and contains one triple bond