Explanation The term utility refers to the total satisfaction or pleasure that a consumer receives from the consumption of a good or service in an economy. The total utility is the summation of all the utilities that a consumer receives from each good or service whereas the marginal utility is an additional utility that a consumer receives from the consumption of an additional unit of commodity or service. The indifference curve denotes different combinations of two goods that provide the same level of satisfaction to the consumer from all the points. Option (c): The marginal rate of substitution when a movement is downward along the indifference curve is the rate at which a consumer is willing to give up the units of Y for X. at first the marginal rate of substitution will be higher whereas when the movement is downwards, the marginal rate of substitution decreases because the marginal utility from the additional unit of X received will decrease as more and more of X is consumed and after the midpoint becomes lower than the given up marginal utility from Y. This means that option 'c' is correct. Option (a): As the consumer moves downward the indifference curve, the consumption of X increases and that of Y decreases...