We have to name this compound. First this is an alkyne because it has a triple bond, then the sufix of the name is yne. It has 4 atoms of C, then this is a butyne.
Then we have two options, we can start counting the C from left to right or from right to left. The rule says that the chlorine must have the lowest number possible. If we count from left to right, the triple bond is between C-3 and C-4 and the chlorine is bonded to C-4. So it name would be 4-chloro-3-butyne.
If we count from right to the left. The triple bond is between C-1 and C-2 and the chlorine is bonded to C-1. The name would be 1-chloro-1-butyne. We are giving with this option to the chlorine the lowest number possible.
Answer: A. 1-chloro-1-butyne.