A consumer maximizes his utility in consuming a good 'X' when

A consumer maximizes their utility in consuming a good 'X' when the marginal utility of the last unit consumed (Mux) is equal to the price of the good (Px). In other words, the consumer will continue to purchase units of the good 'X' until the additional satisfaction received from consuming another unit (Mux) is no longer greater than the price they pay for that unit (Px). This is because if the price of the good is greater than the satisfaction received from consuming it, the consumer would be better off spending their money on something else that gives them more satisfaction per unit of money spent. Alternatively, if the price of the good falls, the consumer is more likely to continue purchasing more units until the Mux equals the new, lower price. On the other hand, if the Mux is greater than the price, the consumer would benefit from consuming more units of the good.