What term describes a state in which someone is unaware and unable to react to their surroundings?

The term that describes a state in which someone is unaware and unable to react to their surroundings is "coma." In this condition, a person exhibits profound unconsciousness, meaning they do not respond to external stimuli and are not aware of themselves or their environment. This state can result from various factors, including severe head injuries, strokes, or certain medical conditions that affect brain function.

In contrast, the other options refer to different medical concepts. Contamination pertains to the presence of harmful substances or pathogens, typically in relation to infection control. Nosocomial refers to infections that are acquired in healthcare settings, such as hospitals, rather than being the result of personal health. Hemiplegia describes paralysis on one side of the body, which does not imply a lack of awareness or responsiveness to the environment. Therefore, "coma" is the most accurate term to describe the given state.