Question

in electrical installations, many device boxes are affixed to what?
wall studs
structural foundations
ceiling brackets
drywall

Explanation:

In standard electrical installations, device boxes (for outlets, switches, etc.) are securely attached to the structural wooden or metal vertical framing members inside walls, which are wall studs. Drywall is the finish surface, not the structural mounting base; structural foundations are for the building's base, not wall devices; ceiling brackets are for ceiling-mounted components, not most wall device boxes.

Answer:

wall studs