What type of consent is given by adults who are mentally competent to make a rational medical decision?

The correct answer is expressed consent. This type of consent involves a clear and definitive agreement from a patient regarding their medical treatment or intervention. An adult who is mentally competent has the legal capacity to understand the information presented about their medical condition, the proposed treatment, the potential risks and benefits, and any alternatives available. When they provide expressed consent, they do so verbally or in writing, indicating their informed choice to proceed with the medical care being recommended.

In contrast, implied consent typically applies in emergency situations where the patient's consent cannot be obtained, and immediate action is necessary to prevent serious harm or death. Emergency consent may also be used when the patient is unconscious or otherwise incapable of expressing their wishes. Substituted consent can occur when a patient's decision-making ability is compromised, and another party, typically a legal guardian or family member, provides consent on their behalf. Given these distinctions, expressed consent is the appropriate term for adults who are capable of making informed medical decisions.