Answer
Option b. neither rising nor falling.
Work Step by Step
Marginal utility is defined as the "extra satisfaction from the consumption of one more unit of some good or service." In simpler words, marginal utility is the difference between the total utility at consecutive consumptions of services or goods.
new total utility = old total utility + marginal utility ____(1)
Where marginal utility keeps changing with every consumption of goods or services
If we take marginal utility = 0 in equation (1), we get new total utility = old total utility, i.e. no change in total utility.
