Final answer:
A perfectly competitive firm is a price taker, while a monopolist is a price maker.
Step-by-step explanation:
A perfectly competitive firm is known as a price taker because the pressure of competing firms forces them to accept the prevailing equilibrium price in the market. In a perfectly competitive market, a firm has no market power and must simply accept the market price as given. On the other hand, a monopolist is a price maker because it has market power and can set its own price based on its assessment of consumer demand.