Final answer:
The severity of the burn is classified as 2) severe. It is likely a third-degree burn that requires medical attention.
Step-by-step explanation:
The severity of the burn in this situation would be classified as 2) severe.
Based on the description of the burn, which includes redness and blisters on the entire upper leg, it is likely a third-degree burn.
Third-degree burns fully extend into the epidermis and dermis, destroying the tissue and affecting the nerve endings and sensory function.
These burns are serious and require medical attention as they will heal slowly without it.
In severe cases, fourth-degree burns can occur, affecting the underlying muscle and bone.
However, the information provided does not indicate this level of severity.