Starting torque is the torque produced by a motor when it is first switched on and starts to rotate. It is an important parameter to consider when selecting a motor for applications that require high starting torque, such as in compressors, pumps, and air conditioners.

The correct answer to the given question is option 'C', which is the capacitor-start motor. This type of motor is specifically designed to provide high starting torque.

The capacitor-start motor is a single-phase motor that uses a capacitor to create a phase shift in the motor's windings. This phase shift creates a rotating magnetic field, which in turn produces the starting torque. The capacitor is connected in series with the start winding of the motor, and it is disconnected from the circuit once the motor reaches a certain speed.

Here are the reasons why a capacitor-start motor has the highest starting torque compared to the other options:

1. Split-phase motor:
- A split-phase motor is another type of single-phase motor that uses a centrifugal switch to create a phase shift and provide starting torque.
- However, the starting torque of a split-phase motor is lower than that of a capacitor-start motor.
- This is because the split-phase motor relies on the difference in impedance between the start and run windings to create a phase shift, which limits the amount of starting torque that can be generated.

2. Shaded pole motor:
- A shaded pole motor is a type of single-phase induction motor that uses a shading coil to create a rotating magnetic field.
- However, shaded pole motors are known for their low starting torque.
- The asymmetrical magnetic field produced by the shading coil results in a lower starting torque compared to other types of single-phase motors.

3. Repulsion motor:
- A repulsion motor is a single-phase motor that uses brushes and commutator to produce starting torque.
- Although repulsion motors can provide high starting torque, they are not as efficient as capacitor-start motors.
- Repulsion motors also require regular maintenance and are more complex in design.

In conclusion, the capacitor-start motor has the highest starting torque among the given options. It is specifically designed to provide high starting torque and is commonly used in applications that require a high initial torque.