The correct answer is D. Inertia.
Mechanical choppers are devices that use a physical switch to turn a power source on and off very quickly. This on-off switching creates a pulsing signal that can be used to control the power to a load.
The chopping rate is the frequency at which the switch is turned on and off. The higher the chopping rate, the more pulses per second are created. This can be useful for controlling the speed of a motor or the brightness of a light.
However, there is a limit to how high the chopping rate can be. This is because the switch has inertia. Inertia is the resistance of an object to changes in motion. The switch needs time to move from one position to the other. If the chopping rate is too high, the switch will not be able to keep up and the signal will become distorted.
The other options are not correct because they do not affect the chopping rate. Input impedance is the resistance of a circuit to current flowing into it. Output impedance is the resistance of a circuit to current flowing out of it. Response time is the time it takes for a circuit to react to a change in input. These factors can affect the performance of a mechanical chopper, but they do not limit the chopping rate.