Which vent is designated for a single fixture or battery of fixtures connected to the same stack?

The correct choice is a unit vent, which is specifically designed to serve a single fixture or a battery of fixtures connected to the same stack. This type of vent allows for the effective removal of gases and odors from the plumbing system associated with the fixtures, ensuring that they operate efficiently. A unit vent is typically connected directly to a fixture and extends vertically to a point where it can effectively vent gases to the atmosphere, facilitating proper air circulation and preventing the build-up of negative pressure that could lead to trap siphoning.

In contrast, local vents and continuous vents do not serve the same purpose. Local vents generally refer to vents that serve only a specific group of fixtures, not singular fixtures. Continuous vents connect multiple fixtures but do so over a longer reach or run than what is feasible for a unit vent. Wet vents, on the other hand, allow for both waste and venting functions in a single pipe run, usually found in situations where multiple fixtures are closely grouped, which is different from the singular focus of a unit vent.