Final answer:
The primary responsibility of friars in missions was teaching Catholicism to Native Americans. They sought to educate and convert natives, with figures like Bartolome de las Casas recognizing and advocating for native societies.
Step-by-step explanation:
The responsibility that best matches that of the friar in a mission is teaching Catholicism to Native Americans. Friars were part of the religious force sent to New Spain to convert natives to Christianity. They educated the Native American population and attempted to bridge gaps between the two societies. Dominicans such as Bartolome de las Casas argued against seeing natives as inhuman or beastly and recognized their organized states and customs. The role of friars expanded beyond merely teaching Catholic doctrines; they were involved in cultivating understanding between the native populations and the Spaniards, though their primary duty was spiritual guidance and conversion.