The correct answer is rate of change of consumption as income changes?.Marginal propensity to consume refers to the change in consumption with respect to the change in income.When there is an increase in income it reflects in better purchasing power of a consumer.The change in income not only affects consumption but also induces changes in savings.The proportion of consumption depends upon the income levels and corresponding necessities of the consumer.It is used widely in economics to calculate the required additional production for the increased demand(consumption).Additional InformationThe complement of the MPC( Marginal propensity to Consume) is Marginal Propensity to Save(MPS).They both reflect the increase in income.Marginal Propensity To Consume (MPC)- In economics, the marginal propensity to consume (MPC) is defined as the proportion of an aggregate raise in pay that a consumer spends on the consumption of goods and services, as opposed to saving it. The marginal propensity to consume is a component of Keynesian macroeconomic theory and is calculated as the change in consumption divided by the change in income. The marginal propensity to consume is equal to ?C / ?Y, where ?C is the change in consumption, and ?Y is the change in income. If consumption increases by 80 cents for each additional dollar of income, then MPC is equal to 0.8 / 1 = 0.8.