For a monopolist, the marginal revenue is less than price whereas marginal revenue is equal to price for a perfectly competitive firm.
When a perfectly competitive firm sells additional units, it can do so at the market price without affecting the price; hence, its marginal revenue equals the price of the product. In contrast, a monopolist has market power and faces a downward-sloping demand curve. This means that to sell more units, the monopolist must lower the price for all units sold, resulting in marginal revenue being less than the price. Therefore, the correct understanding is that while a monopolist’s marginal revenue is not equal to the price, a perfectly competitive firm’s marginal revenue is equal to the price it can charge for additional units.