Final answer:
In a competitive industry, firms produce where price equals marginal cost, resulting in allocative efficiency, whereas a monopolistically competitive firm's output leads to higher prices than marginal revenue. A monopoly produces less and charges more than a competitive market, causing allocative inefficiency and social net benefit loss.
Step-by-step explanation:
The outcomes of competitive markets versus monopoly markets significantly differ due to their structures. In a perfectly competitive market, firms are price takers and produce where price equals marginal cost (P=MC), resulting in allocative efficiency. In contrast, a monopolistically competitive firm sets its output where marginal revenue equals marginal cost (MR=MC), with price being higher than marginal revenue due to the downward-sloping demand curve.
A monopoly will produce a smaller quantity at a higher price compared to perfect competition, leading to a loss of potential social benefits since the price exceeds marginal cost (P>MC), indicating that additional production would provide a net benefit to society. When a new firm enters a monopolistically competitive market, the original firm's demand curve shifts to the left, leading to a reduced output and increased price (Q1 and P1).