When chloe find out clarks secret?

Chloe Sullivan discovers Clark Kent's secret in Season 3 of "Smallville," specifically in the episode titled "Exodus." After witnessing Clark's superhuman abilities and piecing together clues over time, she confronts him about his powers. This revelation deepens their friendship and complicates the dynamics among the main characters, as Chloe must navigate her loyalty to Clark while grappling with the implications of his secret.