A:Answer Yes, this drive can be installed in a 2011 27" iMac. You will need a 3.5" to 2.5" adapter bracket to mount it properly so it won't 'float' and potentially become disconnected.
There may be some EFI (BIOS) issues to contend with, so be sure the iMac is fully updated to at least High Sierra before you make the switch otherwise it may not even recognize the SSD. Finally, depending on the iMac, there may be an issue with the HDD thermal sensing. A special adapter for that may also be required so the fans don't run at full speed all the time.
Good luck!