ANS:A - capacity of the evaporator is decreased.

In a vertical tube evaporator, the liquor level refers to the depth of the liquid in the evaporator vessel. When the liquor level increases:

1. The capacity of the evaporator is typically increased because a higher liquor level means more liquid available for evaporation, allowing for a higher evaporation rate.
2. The true temperature drop (the temperature difference between the heating steam and the boiling liquid) also tends to increase because of the greater liquid depth, which can result in a more significant temperature gradient between the heating medium and the boiling liquid.