Final answer:
The ethical principle that refers to a healthcare professional's duty to avoid causing harm and to be a responsible custodian of public trust is the principle of nonmaleficence.
Step-by-step explanation:
The ethical principle being asked about in the question refers to a healthcare professional's fiduciary duty to be a responsible and faithful custodian of the public trust. The correct answer is b) Non-maleficence. This duty falls under the principle of nonmaleficence, which entails that healthcare professionals should act in ways that do not cause harm to others. This extends to avoiding harm in clinical settings by ensuring that patients are not unnecessarily harmed and that any potential harms from a procedure, treatment, or test are necessary for effective treatment. Furthermore, in research settings, nonmaleficence involves designing trials to minimize harm to participants as much as possible.