Gossip Girl Season 4 Episode 5 (Gossip Girl s04e05) with title “Goodbye, Columbia” aired on Monday, October 11th 2010 at 09:00 pm via CW Network.
Here is summary for Gossip Girl Season 4 Episode 5 :

An anonymous Gossip Girl blast starts a very damaging rumor about one of Columbia’s new students, Serena. On her path to greatness, Blair decides to take a class with a powerful businesswoman, Martha, who is guest-lecturing at Columbia, but a mysterious fellow student thwarts her plans to secure the prized position as Martha’s assistant.