Which of the following is a symptom of dehydration?

Dry mouth is a classic symptom of dehydration because it occurs when the body does not have enough fluid to maintain its normal functions. When hydration levels drop, saliva production decreases, leading to a parched feeling in the mouth. This symptom is one of the first indicators that the body is running low on fluids and is unable to properly hydrate the mucous membranes.

While excessive sweating and increased urination may be associated with fluid loss, they are not direct symptoms of dehydration itself. Instead, they can be responses to heat or other conditions. Hyperactivity is not related to dehydration; in fact, dehydration often leads to fatigue and decreased energy levels. Thus, dry mouth serves as a straightforward and immediate sign that should alert individuals to the need for hydration.