Which of the following is a sign of dehydration in a patient?

Dry mucous membranes are a key indicator of dehydration because they suggest that the body is not retaining adequate fluid levels. When the body is dehydrated, it struggles to maintain moisture in areas such as the mouth and nasal passages, leading to dryness. Other physical signs of dehydration can include reduced sweat production, increased thirst, and in more severe cases, alterations in skin turgor and concentration of urine.

In contrast, increased energy levels and clear urine output typically imply proper hydration and effective renal function, as clear urine usually indicates that the kidneys are filtering adequately and the body is well-hydrated. Moist skin would also signify hydration; individuals who are dehydrated tend to have skin that appears dry and lacking in moisture. Thus, dry mucous membranes serve as a significant, practical indicator of dehydration that healthcare providers can quickly assess.