Final answer:
The white smoke from copper-zinc brazing is likely from a dangerously reactive volatile waxy white solid in the flux, which glows and can ignite in air.
Step-by-step explanation:
The white smoke that can be emitted from copper-zinc brazing alloy is likely due to the presence of a volatile waxy white solid that is used in the flux.
This substance is dangerously reactive in air and can glow with a white light, often spontaneously bursting into flame upon exposure. This reaction is due to the substance's low melting point, at about 44.2°C, which allows it to volatilize and oxidize rapidly when heated during the brazing process.