In a closed-loop process control system, what is meant by the proportional mode of control?

Correct Answer: Option D — It is a control mode that produces a control action that is proportional to the error.

Proportional control is a fundamental mode where the output signal is directly proportional to the magnitude of the error (the difference between the set point and the process variable). The controller gain determines the strength of this response, providing a corrective action that scales linearly with the deviation from the target.