ESCO Brazing and Soldering Practice Test

The flame’s heat and its shape come from the fuel-oxidizer combination. The oxyacetylene flame, produced by burning acetylene with pure oxygen, gives the hottest, most focused flame—often described as a sharp inner cone. Its temperature is in the range around 5400°F, which matches the figure in the question. This makes it the best match for a sharp, very hot flame among the options. Other fuels burn cooler or produce different flame profiles in typical brazing conditions, so they don’t fit the description as well.