What is the structural formula for propyne?

Propyne is an alkyne with three carbon atoms, and the presence of a triple bond is a defining characteristic. The correct structural formula for propyne must reflect this triple bond between the first two carbon atoms.

The formula identified as the correct answer shows a triple bond between the first and second carbon atoms, represented as CH≡C-CH₃. This notation clearly indicates that the first carbon (C1) is bonded by a triple bond to the second carbon (C2) and has an additional single bond to a third carbon (C3), which bears three hydrogen atoms, thus completing the alkane environment for C3.

The other options do not represent propyne accurately as they either depict the wrong structure or do not account for the position of the triple bond correctly. For instance, while CH₃-C≡C-H indicates a valid alkyne structure (but would be 1-butyne rather than propyne), the distinction lies in where the triple bond is located in relation to the carbon atoms. The option CH₂≡C-CH₂-CH₃ describes a compound with four carbons, which is not propyne but a similar compound with a different carbon count.