Answer: Income effect
Explanation: The Income effect could simply be explained as the impact of price on an individual's income which ultimately affects the demand for certain products. Using the scenario above as a case study,Assuming Manuel's income remains constant, the increase in price of Manuel's favorite, donut increases, this increase in price will lead to a decrease in Manuel's purchasing power as Manuel's income tends to suffer or diminish more due to the price increase. Therefore, in other to contain this effect, Manuel will have reduce his consumption, hence leading to lower demand for goods including that of donut.