Final answer:
The correct stage at which antiviral medications target HIV during viral entry is the fusion stage, where fusion inhibitors prevent the HIV viral envelope from fusing with the host cell membrane.
Step-by-step explanation:
The viral entry of antiviral medication used to treat HIV focuses on several stages of the virus's replication cycle. Among them, the stage at which fusion inhibitors work is during the fusion of the HIV viral envelope with the plasma membrane of the host cell. This is when the virus's envelope fuses with the cell membrane, allowing the viral contents to enter the host cell. Therefore, the correct answer to the question would be option 2) Fusion.