The correct answer is option C: torque.

Induction motors are the most commonly used type of motor in various industrial and commercial applications. These motors work on the principle of electromagnetic induction. The stator windings of the motor are connected to an AC power supply, which creates a rotating magnetic field. This rotating magnetic field induces currents in the rotor windings, causing the rotor to rotate.

When the supply voltage to the induction motor is increased, several parameters of the motor are affected. Let's discuss each option in detail:

a) Power factor:
The power factor of an induction motor is the ratio of real power (wattage) to apparent power (volt-ampere). An increase in supply voltage does not directly affect the power factor of the motor. The power factor depends on the load connected to the motor and the motor design. Therefore, option A is incorrect.

b) Slip:
Slip is defined as the difference between the synchronous speed and the actual rotor speed of the motor. It is expressed as a percentage. An increase in supply voltage does not directly affect the slip of the motor. The slip primarily depends on the load torque and the rotor resistance. Therefore, option B is incorrect.

c) Torque:
Torque is the rotational force produced by the motor. An increase in supply voltage directly affects the torque produced by the motor. The torque is directly proportional to the square of the supply voltage. Therefore, with an increase in supply voltage, the torque produced by the motor increases. This is because the increased voltage results in a stronger magnetic field, which in turn generates a higher torque. Therefore, option C is correct.

In conclusion, with an increase in supply voltage, the torque produced by the induction motor increases. The power factor and slip of the motor are not directly affected by the increase in supply voltage.