Final answer:
The pair most likely to have a negative cross-price elasticity of demand is margarine and butter, indicating they are complementary goods. A price increase in one leads to a consumption decrease in the other.
Step-by-step explanation:
The pair of items most likely to have a negative cross-price elasticity of demand is b) margarine and butter. This indicates that the two goods are complements, meaning that they are often used together. When the price of one good increases, the demand for the other good is likely to decrease because the more expensive item is being bought less, and therefore, the complementary item, which is used with it, will also be bought less. Put simply, if the price of butter goes up and people buy less butter, they are also likely to reduce their purchase of margarine, as they are often used for the same purpose.
According to the cross-price elasticity of demand, if goods A and B are substitutes, like tea and coffee, an increase in the price of B (coffee) will increase the consumption of A (tea), showing a positive cross-price elasticity. However, if goods are complements, like hot dogs and mustard, an increase in the price of hot dogs would typically decrease the quantity demanded of hot dogs, leading to a decrease in mustard consumption as they are used together, demonstrating a negative cross-price elasticity.