A rational consumer purchases a product up to the point where price equals marginal utility.Explanation: A rational consumer always aims to maximise total satisfaction from limited income. For every unit of a product, the consumer compares the market price with the marginal utility, which is the extra satisfaction gained from that unit. If the price is less than marginal utility, the consumer gains a surplus and should buy more units. If the price is greater than marginal utility, the consumer loses satisfaction and will not buy that unit. Therefore, the best point of purchase is when the price is exactly equal to marginal utility. At this point, the consumer is in equilibrium because there is no reason to buy more or less. This is expressed as P=MU.Answer: C. equal to his marginal utility