Correct Answer - Option 3 : Helium welding
Resistance welding is the process of joining two metals together by the heat produced due to the resistance offered to the flow of electric current at the junction of two metals.
Depending upon the method of weld obtained and the type of electrodes used, resistance welding is classified as
1) Spot welding
2) Seam welding
3) Projection welding
4) Butt welding
Flash welding is a type of Butt welding.
Helium welding is not a type of resistance welding.