The correct answer is option 'B': plant reserve capacity will be zero.

Explanation:
In a power plant, the maximum demand refers to the highest amount of power consumed by the load at any given time. Plant capacity, on the other hand, refers to the maximum amount of power that the power plant is capable of generating.

When the maximum demand on the power plant is equal to the plant capacity, it means that the load is consuming power at its maximum capacity. This scenario has a few implications:

1. Load factor:
The load factor is the ratio of the average power demand to the maximum power demand over a specific period of time. In this case, since the maximum demand is equal to the plant capacity, the load factor will be 1 (or 100%). This is because the load is consuming power at its maximum capacity all the time, resulting in a load factor of unity.

2. Plant reserve capacity:
Plant reserve capacity refers to the additional power generation capacity that is available in the power plant beyond the current load requirements. It acts as a buffer to meet unexpected increases in demand or to provide backup power during maintenance or emergencies. In this scenario, when the maximum demand is equal to the plant capacity, there is no reserve capacity available. The plant is operating at its maximum capacity, leaving no additional capacity for unexpected increases in demand.

3. Diversity factor:
Diversity factor is the ratio of the sum of individual maximum demands to the maximum demand on the power plant. It represents the extent to which the maximum demands of individual loads occur simultaneously. In this case, since the maximum demand on the power plant is equal to the plant capacity, the diversity factor will be unity. This means that the maximum demands of individual loads occur simultaneously and are equal to the maximum demand on the power plant.

In summary, when the maximum demand on a power plant is equal to the plant capacity, the load factor will be unity, the plant reserve capacity will be zero, and the diversity factor will be unity.