The correct answer is Option 3: b, c and d
a) When TU (Total Utility) is rising at an increasing rate, MU (Marginal Utility) also rises. False. The Law of Diminishing Marginal Utility states that as more units of a good are consumed, the additional satisfaction (marginal utility) derived from each successive unit tends to decrease. If TU is rising at an increasing rate, it would imply MU is increasing, which contradicts the fundamental law of diminishing marginal utility that usually governs consumer behavior. Total utility typically rises at a decreasing rate (meaning MU is positive but falling).
b) When TU (Total Utility) is rising at decreasing rate, MU (Marginal Utility) falls. True. This is the standard relationship. As long as total utility is increasing, marginal utility is positive. However, due to the Law of Diminishing Marginal Utility, the rate at which total utility increases slows down. This "decreasing rate" of increase in TU corresponds to a falling (but still positive) MU.
c) MU (Marginal Utility) falls due to Law of Diminishing Marginal Utility. True. This is the definition and core principle of the Law of Diminishing Marginal Utility. It explicitly states that as consumption of a good increases, the marginal utility derived from each additional unit decreases.
d) When TU (Total Utility) is maximum, MU (Marginal Utility) is 0. True. At the point where total utility reaches its peak, consuming an additional unit provides no extra satisfaction, meaning the marginal utility of that unit is zero. If you consume beyond this point, total utility would start to fall, and marginal utility would become negative. | 
