The correct answer is: B. An additional unit of consumption will decrease total utility.
Marginal utility is the change in total utility that results from consuming one additional unit of a good or service. When marginal utility is zero, it means that consuming one additional unit of the good or service will not increase total utility. In other words, the consumer is already getting all the satisfaction they can from consuming the good or service.
If marginal utility is negative, it means that consuming one additional unit of the good or service will actually decrease total utility. This can happen if the consumer is consuming too much of the good or service and is starting to feel sick or uncomfortable.
When marginal utility is positive, it means that consuming one additional unit of the good or service will increase total utility. This is the case when the consumer is not consuming enough of the good or service and is still getting satisfaction from consuming more.
In conclusion, if marginal utility is zero, then an additional unit of consumption will decrease total utility.