An alkyne is defined as a molecule with at least one triple bond in it, for the chemical formula, to find an alkyne we can do with the following set up:
CnH2n-2
Where C is the number of Carbons, H is the number of Hydrogens and n is the number of atoms
The only option that fits this configuration is C3H4, where we have 3 atoms of Carbon, and (2 * 3) - 2 Hydrogens, 6 - 2 = 4
Therefore the answer will be letter A