Brutus accuses Cassius of being corrupt. Option 2 is correct.
In the story, Brutus refered openly to how Cassius is untrustworthy due to the fact that he received a lot of bribe from merchants and people from other kingdom. Brutus was seeking to damage public's perception regarding Cassius and make them doubt Cassius' credibility.
Brutus is the most complex character in Julius Caesar and is also the play's tragic hero.
Cassius is described as a manipulative man who uses Brutus's good nature and character in an attempt to destroy the life of Julius Caesar.