Final answer:
Severe dehydration in infants is indicated by symptoms such as tachycardia, parched mucous membranes, and sunken eyes and fontanels.
Step-by-step explanation:
When evaluating the extent of an infant's dehydration, severe dehydration is characterized by tachycardia, parched mucous membranes, and sunken eyes and fontanels. Tachycardia refers to an abnormally fast heart rate, while parched mucous membranes indicate dryness of the mouth and throat. Sunken eyes and fontanels, which are the soft spots on a baby's head, suggest significant fluid loss.