Final answer:
Mastercard prohibiting a merchant from accepting other credit cards if it wants to accept Mastercard is an example of tying. a)Tying sales are a restrictive practice where consumers are forced to buy one product to get another, which can limit competition and consumer choice.
Step-by-step explanation:
If Mastercard prohibits a merchant from accepting other credit cards if it wishes to be able to accept Mastercard from customers, this is an example of tying. Tying sales are a form of restrictive practices which reduce competition and can be controversial. These practices force consumers to buy a product only if they also buy another product.
Tying sales are criticized because they compel consumers to purchase products they may not want. For instance, if to purchase a popular DVD, a store mandates that you also buy a certain model of a portable TV, consumers are forced into buying an associated product without the freedom to choose from other available options in the market.
Antitrust authorities prevent firms from colluding to reduce competition, and tying sales can sometimes be seen as a way to circumvent antitrust laws, resulting in investigations and cases related to such restrictive practices.