Final answer:
In the long run of a perfectly competitive market, firms reach an equilibrium where economic profits are driven down to zero. However, each firm may still earn negative accounting profit if implicit costs are positive.
Step-by-step explanation:
In the long run of a perfectly competitive market, firms will react to profits by increasing production and to losses by reducing production or exiting the market. This process will continue until the market reaches long-run equilibrium, where no new firms want to enter the market and existing firms do not want to leave.
At this equilibrium, economic profits are driven down to zero. However, it is important to note that zero economic profit is not equivalent to zero accounting profit. Each firm operating in the industry in the long run may still earn negative accounting profit if implicit costs are positive.