Final answer:
The principle of beneficence is the embodiment of the Belmont Report's mandate to protect the welfare of research participants.
Step-by-step explanation:
The Belmont Report's mandate that the welfare of research participants must be protected is embodied in the principle of beneficence. Beneficence means acting in ways that benefit others or are for the good of others. In research settings, beneficence is achieved by considering the interests of participants, treating them fairly, and prioritizing their well-being alongside scientific advancement.