Questions: A firm in an industry with a differentiated product, many sellers, and zero economic profit in the long run is: a monopoly. perfectly competitive. an oligopoly. monopolistically competitive.

The answer is monopolistically competitive.

A monopoly is a market structure where there is only one seller in the market, and the firm has significant control over the price. Monopolies can earn economic profits in the long run due to barriers to entry that prevent other firms from entering the market.

A perfectly competitive market is characterized by many sellers offering identical products, with no single firm having any control over the market price. In the long run, firms in a perfectly competitive market earn zero economic profit due to the free entry and exit of firms.

An oligopoly is a market structure with a few large firms that dominate the market. These firms may sell identical or differentiated products, and they have some control over the prices. Oligopolies can earn economic profits in the long run due to barriers to entry.

A monopolistically competitive market is characterized by many sellers offering differentiated products. In the long run, firms in a monopolistically competitive market earn zero economic profit because of the free entry and exit of firms, which erodes any short-term economic profits. This aligns with the conditions described in the question.