Loss of memory or concentration is a/an ____ reaction to stress.

The correct answer is cognitive because loss of memory or concentration directly pertains to mental processes. Cognitive reactions to stress involve changes in how a person thinks, processes information, and remembers experiences or details. When an individual is under significant stress, it can affect their ability to focus, leading to difficulties in remembering information or concentrating on tasks.

In contrast, physical reactions involve bodily responses to stress, such as increased heart rate or muscle tension. Emotional reactions refer to feelings such as anxiety or irritability experienced during stressful situations. Behavioral reactions are about changes in actions, such as withdrawing from social interactions or exhibiting restlessness. Since loss of memory and concentration are specifically linked to mental functioning, cognitive is the most appropriate descriptor.