Final answer:
Flames are first visible during the free-burning stage of a fire. This stage is marked by visible flames, in contrast to earlier stages where combustion may occur without visible fire.
Step-by-step explanation:
At which stage of a fire are flames first visible? The correct answer is a) Free-burning stage. The free-burning stage is characterized by the production of visible flames. In contrast, the incipient stage is when a fire has just ignited and may not be visible, the uncontrolled stage is a broader term that can refer to any point at which the fire is burning without restraint, and the smouldering stage is the initial phase where the material is slowly beginning to burn without visible