Concept:When total utility does not change as more units are consumed, the extra utility from the last unit is zero.
Explanation:Total utility
(TU) is the sum of satisfaction from all units consumed.
Marginal utility
(MU) is the additional satisfaction from consuming one more unit.
As consumption increases,
MU falls due to the law of diminishing marginal utility.
When
TU reaches its maximum, it becomes constant.
At that point, the next unit adds no extra satisfaction.
Therefore,
MU=0.
This is the saturation point of consumption.
Answer:B. zero