Final answer:
A serious problem common only to three-phase motors is single-phasing. (option B)
Step-by-step explanation:
A serious problem common only to three-phase motors is single-phasing. When a motor is single-phased, it loses its ability to generate the required magnetic field and can cause overheating, decreased efficiency, and potential damage to the motor. Single-phasing is a condition in which one of the three phases in a three-phase motor fails to supply power properly. This can happen due to various reasons such as a faulty power supply, damaged wiring, or a blown fuse. When a motor is single-phased, it loses its ability to generate the required magnetic field and can cause overheating, decreased efficiency, and potential damage to the motor.
For example, if a motor is designed to operate on a three-phase power supply but one of the phases fails, the motor will experience reduced power output and may overheat due to the unbalanced operating conditions.