Which of the following lesions is an open sore that may involve the dermis and can contain pus?

An ulcer is characterized as an open sore that can penetrate the epidermis and extend into the dermis, making it more severe than superficial skin lesions. It often features a base that may be moist and can contain pus, indicating potential infection or inflammation. This type of lesion results from the breakdown of skin tissue, often due to factors such as pressure, poor circulation, or infections.

Understanding this definition is essential in distinguishing ulcers from other types of lesions. A fissure, for example, is a small, linear crack in the skin that does not extend significantly into deeper layers. A blister is a fluid-filled sac that forms between layers of skin but does not typically involve pus and is primarily a response to friction or irritation. A scale refers to dry or flaky skin and does not involve an open sore. Thus, the defining characteristics of an ulcer make it the correct choice in this context.