Step 1: Sort the four processes by their basic heat source.
Electron beam welding gets its heat from a focused stream of fast moving electrons, and laser beam welding gets its heat from a concentrated beam of coherent light, so both belong to the high energy beam welding family rather than arc welding. Thermit welding gets its heat purely from an exothermic chemical reaction between aluminium powder and iron oxide, with no electrical arc involved at all.
Step 2: Look closely at how electroslag welding actually starts and runs.
Electroslag welding is used for joining very thick sections in the vertical position, and although its main heating during the run comes from electrical resistance heating of a molten slag bath, the process cannot begin that way, an electric arc has to be struck first at the bottom of the joint to melt the initial flux and build up that molten slag pool.
Step 3: Decide which process qualifies as an arc welding type.
Because it depends on an electric arc to get going and relies on electrical energy throughout, electroslag welding is grouped together with, or treated as closely related to, arc welding processes, unlike the beam based or purely chemical processes in the other options. Among the four choices, it is the only one connected to an electric arc in any way.
\[ \boxed{\text{Electro slag welding}} \]