Which of the following is a sign of a severe burn?

Charred skin is a definitive indicator of a severe burn, often associated with third-degree burns, which destroy both the outer layer of skin and underlying tissues. This level of burn typically results from prolonged exposure to extreme heat sources, such as flames or hot objects, leading to the coagulation of skin proteins and the destruction of nerve endings in the affected area, which can also lead to a lack of pain sensation at the burn site due to nerve damage.

In contrast, other signs mentioned, such as redness, blistering, and pain, may indicate less severe burns. Redness usually signifies first-degree burns, which affect only the outer layer of skin, while blistering is indicative of second-degree burns, which affect deeper layers of skin but do not usually reach the point of charring. Pain is often present in varying degrees across all burn types but does not alone signify the severity of the burn. The presence of charred skin clearly indicates that the injury has reached a severe level, involving extensive tissue damage and a greater risk for complications.