What term describes an individual's ability to make rational decisions regarding their own well-being?

The term that best describes an individual's ability to make rational decisions regarding their own well-being is "competent." Competence refers to the legal and clinical assessment of a person's ability to understand information related to their health status and the implications of their choices, including the ability to appreciate the consequences of their decisions.

In a medical context, a competent person can communicate and express their preferences, understand the information presented to them, reason about treatment options, and provide informed consent. This is crucial in situations such as emergency care, where quick and informed decisions may need to be made regarding treatment, interventions, or refusal of care.

While the other options might seem relevant, they do not carry the same legal and clinical implications as competence. "Capable" often refers to a more general ability to perform tasks but is less specific regarding decision-making associated with well-being. "Sound" generally describes reasoning or judgment that is logical and reasonable but lacks the specific legal context. "Rational" relates to the thought process itself, but does not encompass the overall capacity to make decisions that are informed and understood fully in medical scenarios.