In perfect competition, a firm does not exercise control over price. This is because perfect competition is characterized by a large number of small firms that produce identical products and have no market power. Here is a detailed explanation:

Perfect Competition:
- In perfect competition, there are many buyers and sellers in the market, and each firm produces an identical product.
- The market is characterized by free entry and exit, meaning that new firms can easily enter the market and existing firms can exit if they are not making a profit.
- The price in a perfectly competitive market is determined by the forces of supply and demand. Each firm is a price taker, meaning that it has to accept the market price as given and cannot influence it.
- The demand curve faced by a perfectly competitive firm is perfectly elastic, meaning that the firm can sell as much as it wants at the market price, but cannot sell at a higher price.
- As a result, a perfectly competitive firm has no control over the price of its product. It can only determine the quantity it wants to produce based on its profit maximization objective.

Other Market Forms:
- In contrast, in a monopoly, there is a single firm that is the sole provider of a product or service in the market. The firm has significant market power and can set the price of its product.
- In an oligopoly, there are few large firms in the market, and each firm has some degree of market power. They may engage in strategic behavior and consider the actions of other firms when making pricing decisions.
- In monopolistic competition, there are many firms in the market, but each firm produces a slightly differentiated product. The firms have some degree of market power and can set prices based on product differentiation.
- In all these market forms, the firms have some control over the price of their product, unlike in perfect competition.

Therefore, it can be concluded that in perfect competition, a firm does not exercise control over price. The market forces of supply and demand determine the price, and each firm is a price taker.