What is the structural formula for 2-butyne?

The structural formula for 2-butyne is indeed represented by CH₃-C≡C-CH₃.

In this compound, the "2-" designation indicates that the triple bond occurs between the second and third carbon atoms in the butyne chain. The longest continuous carbon chain contains four carbons (hence the prefix "but-"), and the presence of a triple bond in this molecule characterizes it as an alkyne.

To visualize it, there are two methyl groups (CH₃) attached to the terminal carbon atoms of a chain of four carbons, with the triple bond situated between the second and third carbon. This arrangement meets the criteria for the full structural formula of 2-butyne.

The other options do not represent 2-butyne accurately. For instance, the formula in one option suggests a double bond, which is characteristic of alkenes rather than alkynes. Another option lists a molecular formula without detailing the specific structure, which doesn’t provide a clear representation of the triple bond positioning needed to identify it as 2-butyne. Thus, option A is the correct choice, as it clearly depicts both the position of the triple bond and the overall structure of 2-b