Which of the following describes a bathroom group?

A bathroom group is specifically defined as a collection of fixtures that serve the purpose of personal hygiene. This typically includes essential fixtures such as a water closet (toilet), a lavatory (sink), and sometimes a bathtub or shower. The primary function of these fixtures is to provide facilities for washing, bathing, and other personal care activities, making option C the most accurate description of a bathroom group.

Other choices describe different types of fixtures or installations. For instance, kitchen fixtures are pertinent to food preparation and cleaning areas, while plumbing appliances may include items that are not specifically related to personal hygiene. Outdoor plumbing installations would encompass a variety of plumbing fixtures and systems that are not limited to bathroom use, therefore not correctly identifying a bathroom group. Thus, the focus on personal hygiene clearly identifies why C is the correct answer.