The correct answer is B.
The utilization factor is the ratio of the average load on a power plant to its installed capacity. It is a measure of how efficiently a power plant is being used. A utilization factor of 1 means that the power plant is being used at its full capacity. A utilization factor of less than 1 means that the power plant is not being used at its full capacity.
If a power plant has a maximum demand more than its installed rated capacity, then the utilization factor will be less than 1. This is because the power plant will not be able to meet the maximum demand all of the time.
Option A is incorrect because the utilization factor cannot be equal to unity if the power plant has a maximum demand more than its installed rated capacity.
Option C is incorrect because the utilization factor cannot be more than unity. This is because the utilization factor is a measure of how efficiently a power plant is being used, and a power plant cannot be used more efficiently than its full capacity.
Option D is incorrect because the utilization factor is a well-defined concept in power plant engineering.