Concept:When a fuel gas burns in oxygen, it produces a high-temperature flame that can be controlled for industrial use.
Explanation:The gas involved is acetylene (
C2H2).
When acetylene mixes with oxygen, it burns to give an oxy-ethylene flame.
This flame is extremely hot, reaching above
3000∘C, and it remains steady and controllable.
Because of this intense heat, the flame is able to melt and join metals.
Therefore, it is used mainly for cutting and welding metals.
Answer:Oxy-ethylene flame; cutting and welding metals (Option D).