Idk which FRIENDS TV show you guys are all watching, but at the end of season 7, Monica and Chandler get married and Rachel tells Monica and Phoebe that she's pregnant. She also takes a test at the wedding ceremony. And then in season 8 she tells Ross he's the father :)
The answer is 7. "The one where Monica and chandler get married pt 2" is the last episode of season 7. We find out it's neither phoebe nor Monica pregnant and the camera pans to Rachel. Then season 8 Rachel is pregnant. Gives birth last episode of season 8 Emma is born. Boom.
Answer should be none.. because.. chandler proposed monica at the last of season 7.. they got married at the last of season 8.. then only Rachel got to know that she is pregnant at monica and chandler's wedding ceremony..