Final answer:
A perfectly competitive firm is a price taker and cannot set its own prices due to market forces, whereas a monopolistic competitor can adjust prices due to the availability of substitutes, indicating some market power.
Step-by-step explanation:
The student is referring to different types of market structures and the abilities of firms within these structures to set prices. In a perfectly competitive market, firms are price takers and must accept the market price determined by supply and demand. They face a perfectly elastic demand curve, meaning they can sell any quantity at the market price but cannot influence the price itself.
In contrast, a monopolistic competitor faces a downward-sloping demand curve, indicating the firm can raise its price without losing all its customers due to the presence of substitutes. Thus, a monopolist can increase prices with fewer lost customers compared to a perfectly competitive firm but more than a monopoly.
Additionally, it is important to note that a perfectly competitive firm sells standardized or undifferentiated products and has no market power, whereas a monopolistic competitor sells differentiated products and has some degree of market power.