The speed will be the synchronous speed of the motor if slip becomes Zero. The slip of an Induction motor can never be zero.This is because
1. If the rotor speed and stator speed will equal where will no change is flux linking with the rotor, and hence no current flow through the rotor conductor, resulting no torque or force.
2. In motors the number of rotor slots and stator slots are different and thus cogging (magnetic locking) can’t happen. And thus The slip motor can’t run at rated speed.