Awelding torch produces a flame by burning acetylene fuel in the presence of oxygen the energy released from the acetylene fuel is then used to melt a metal which energy transformation happens during this process

Answer : Chemical energy to thermal energy

Explanation : When the welding torch uses the acetylene fuel for producing flame it is using the chemical acetylene to generate energy in form of light, after the flame is produced the fuel is used for melting a metal which is utilizing the thermal energy. So the ultimate final product is generated from chemical to thermal and so the energy transformation is from chemical energy to thermal energy.

Talc (french chalk) is the ingredient