Answer:
Prosocial behaviour; altruism.
Step-by-step explanation:
As the exercise briefly differenciates, a prosocial behavior is to act to benefit another. Even though at first altruism sounds the same, it is different because it's an act made with no regard for one's safety or interests.
A prosocial behavior would be to act in benefit of other people; helping, sharing, volunteering, etc.
Altruism, on the other hand, is a moral practice which has it's bases in a concern for happiness of every other living being, human or animal. In this case, taken into the extreme, altruism is considered a selflessness synonym.