For Facebook, Tuesday is being seen as a kind of dreaded final exam.

That’s when Mark Zuckerberg, the company’s chief executive, will swap out his trademark gray T-shirts for a suit and tie, and embark on a two-day marathon of testimony on Capitol Hill. His goal? To apologize for Facebook’s missteps, reassure Congress that Facebook intends to stop foreign powers from using its service to meddle in American elections and detail the company’s plans to better protect its users’ privacy.

In preparation for Mr. Zuckerberg’s testimony, his first such appearance, Facebook has spent the last couple of weeks trying to transform its public image from a defiant, secretive behemoth into a contrite paragon of openness, announcing a string of new privacy and anti-abuse measures and making company executives available for numerous interviews.

It has also hired a team of experts, including a former special assistant to President George W. Bush, to put Mr. Zuckerberg, 33, a cerebral coder who is uncomfortable speaking in public, through a crash course in humility and charm. The plan is that when he sits down before the Senate Commerce and Judiciary committees on Tuesday, Mr. Zuckerberg will have concrete changes to talk about, and no questions he can’t handle.

“For every major C.E.O., and now for Mark Zuckerberg, this is a rite of passage,” said Reed E. Hundt, a former chairman of the Federal Communications Commission. “Facebook has become so important — not just to business but to society — it can’t avoid having to run the congressional gantlet.”