The correct answer is C. positive and increasing.
Marginal utility is the additional satisfaction or benefit that a consumer receives from consuming one more unit of a good or service. Total utility is the total satisfaction or benefit that a consumer receives from consuming all units of a good or service.
When total utility increases, marginal utility is positive and increasing. This is because the consumer is receiving more satisfaction from each additional unit of the good or service. As the consumer consumes more and more units of the good or service, the satisfaction they receive from each additional unit decreases. This is because the consumer becomes less and less hungry or thirsty, or less and less interested in the good or service.
Option A is incorrect because marginal utility cannot be negative and increasing. Marginal utility is the additional satisfaction or benefit that a consumer receives from consuming one more unit of a good or service. If marginal utility is negative, then the consumer is receiving less satisfaction from each additional unit of the good or service. This is not possible, as consumers always want to consume more of something that gives them satisfaction.
Option B is incorrect because marginal utility cannot be negative and declining. Marginal utility is the additional satisfaction or benefit that a consumer receives from consuming one more unit of a good or service. If marginal utility is negative, then the consumer is receiving less satisfaction from each additional unit of the good or service. As the consumer consumes more and more units of the good or service, the satisfaction they receive from each additional unit decreases. This means that marginal utility is declining. However, marginal utility cannot be both negative and declining, as this would mean that the consumer is receiving less satisfaction from each additional unit of the good or service, but the total satisfaction they receive from consuming all units of the good or service is increasing. This is not possible.
Option D is incorrect because marginal utility cannot be positive and declining. Marginal utility is the additional satisfaction or benefit that a consumer receives from consuming one more unit of a good or service. If marginal utility is positive, then the consumer is receiving satisfaction from each additional unit of the good or service. As the consumer consumes more and more units of the good or service, the satisfaction they receive from each additional unit decreases. This means that marginal utility is declining. However, marginal utility cannot be both positive and declining, as this would mean that the consumer is receiving satisfaction from each additional unit of the good or service, but the total satisfaction they receive from consuming all units of the good or service is decreasing. This is not possible.