What is the name of this molecule?

But-1-yne

Explanation:

The IUPAC nomenclature of alkynes are given as follows:

Select the longest possible carbon chain.

For the number of carbon atom, we add prefix as 'meth' for 1, 'eth' for 2, 'prop' for 3, 'but' for 4, 'pent' for 5, 'hex' for 6, 'sept' for 7, 'oct' for 8, 'nona' for 9 and 'deca' for 10.

The numbering starts from the end from where the double or triple bond gets lower number. A suffix '-yne' is added at the end of the name after the position of the triple bond.

Hence, the name for given hydrocarbon will be But-1-yne.