Final answer:
Advertising plays a crucial role in differentiating a firm's products, allowing them to obtain loyal customers.
Step-by-step explanation:
In the framework of monopolistic competition, advertising plays a crucial role in differentiating a firm's products from its competitors. When customers believe that a firm's product is unique, it allows the firm to obtain loyal customers. This is because the perceived uniqueness of the product creates a sense of value and differentiation in the minds of customers, leading to increased customer loyalty.