The correct answer is: D. Shaded pole motor
A shaded pole motor is a type of single-phase induction motor that is normally free from mechanical and magnetic vibrations. It has two poles, one of which is shaded by a copper band. The shaded pole creates a magnetic field that is out of phase with the field of the other pole. This creates a rotating magnetic field that causes the motor to turn.
Split phase motors, universal motors, and hysteresis motors all have some degree of mechanical and magnetic vibrations.
A split phase motor has two windings, a main winding and a starting winding. The main winding is connected to the power supply, and the starting winding is connected to the power supply through a capacitor. The capacitor creates a phase shift between the two windings, which creates a rotating magnetic field that causes the motor to turn.
A universal motor is a type of induction motor that can be operated on either AC or DC power. It has a stator with two windings, a main winding and a field winding. The main winding is connected to the power supply, and the field winding is connected to the power supply through a commutator and brushes. The commutator and brushes reverse the polarity of the field winding, which allows the motor to operate on either AC or DC power.
A hysteresis motor is a type of synchronous motor that has a rotor made of a ferromagnetic material that is magnetized by a stator field. The rotor is free to rotate, and it will rotate at the same speed as the stator field.
All of these motors have some degree of mechanical and magnetic vibrations. The shaded pole motor is the only motor that is normally free from these vibrations.