That's not information which can be readily looked up, not to mention that serial numbers are not unique to one firearm - a make and model would be needed, as well.
Contact your local police department and give them the serial number. The Police can check on the stolen gun list maintained by the BATFE. If the gun is stolen, the Police will conficate the piece and begin investigation of how it was acquired.
No way to answer. Sorry.
Contact your local police. If it was reported stolen, it should be in the system.
No.
No. You won't be returned a firearm which has the serial number removed.
Yes, it is possible as long as it is a registered gun that was obtained legally.
Go back to the store where you bought it.
Have the police run the serial number.
Go to the seller where you purchased the gun.
If you think it's stolen, ask the police to run the serial number.
Go to the local police with the serial number.
Ask your local police to run it.