Final answer:
Perfect competition occurs when there are many firms producing identical products, many buyers and sellers, full information availability, and free market entry and exit. Imperfect competition, including monopolistic competition, oligopoly, and monopoly, arises when these conditions aren't met.
Step-by-step explanation:
If all conditions for a perfectly competitive market are met, the outcome is perfect competition. This is characterized by (1) many firms producing identical products; (2) many buyers and sellers interacting in the market; (3) all parties having full information to make rational decisions; and (4) free entry and exit in the market with no restrictions. These conditions ensure that no single firm can control the market price, leading to an optimal allocation of resources where goods are produced at the lowest possible cost and sold at prices that reflect only the cost of production.
In contrast, when any of these conditions are not met, the market structure falls under imperfect competition, which includes monopolistic competition, oligopoly, and monopoly. Monopolistic competition is a market with many firms selling similar but differentiated products, whereas oligopoly is characterized by a few firms that may dominate the market, often leading to strategic interactions regarding pricing and production decisions. Lastly, a monopoly exists when only one firm controls the entire market for a good or service.