Season 4, Episode 10 (Series Episode 63): Branch Wars
It is implied that they broke up in "The Job" but it is specifically addressed in "Fun Run"
yes
Karen Fillipelli who was played by Rashida Jones
Season 5, Episode 2: Business Ethics
The episode is called "gay witch hunt"
Product Recall. Season 3, Episode 20.The episode actually starts with Jim impersonating Dwight.Then, vice versa at the end of the episode.
Lovefool- the kardigans
Season 3, Episode 18: The Negotiation.
Season 4, Episode 13 the name of it is Job Fair
The very first episode, Season 1 "Pilot"
season 3 episode 13 half way through the episode
season 3 episode 20 "product recall"