Final answer:
The arc welding process efficient for joining attachments to planar surfaces is Stud Arc Welding, a variant of Shielded Metal Arc Welding (SMAW) due to its versatility and effectiveness.
Step-by-step explanation:
The arc welding process that provides a very efficient means of joining attachments to planar surfaces is Stud Arc Welding, which is a technique under the umbrella of shielded metal arc welding (SMAW). While not explicitly listed in the options provided, stud welding is most closely related to SMAW. Shielded metal arc welding uses a flux-coated electrode to create an electric arc between the electrode and the workpieces, which melts both the metals to be joined and the electrode's coating to create a weld pool protected by sl ag. Although not as commonly used for precise or critical work, SMAW is preferred for its versatility and ability to weld thick sections and is commonly used in construction and repair work.