Which preposition best describes an action done for someone else's benefit?

The preposition that best describes an action done for someone else's benefit is "on behalf." This phrase is often used to indicate that someone is acting or speaking in the interest of another person, group, or cause. For example, if someone says they are making a decision on behalf of their team, it means they are representing the team's interests and making choices that will benefit them.

The other choices do not convey the same meaning. "In moderation" refers to doing something within reasonable limits, which does not imply any benefit to others. "By process" suggests a method or means of doing something rather than focusing on the intentions behind actions. "For the good of" implies a broader purpose that could be more self-serving or collective rather than specifically for another person. Therefore, "on behalf" is the most direct and appropriate choice when describing an action taken for another's benefit.