Final answer:
Marginal revenue for a competitive seller is equal to the constant market price, while for a monopolist, marginal revenue fluctuates and requires lowering the price to increase sales.
Step-by-step explanation:
The subject of this question is the concept of marginal revenue in different market structures. Specifically, the question compares how marginal revenue behaves in perfectly competitive markets versus in a monopoly situation. In a perfectly competitive market, marginal revenue for the seller is constant and equal to price because increasing output does not affect the market price. This is due to the fact that individual firms are too small to influence the market price. On the other hand, for a pure monopolist, marginal revenue is not constant and reflects the necessity of lowering the price to sell more output. This is because a monopolist faces a downward-sloping demand curve, meaning that to sell additional units, the price must be reduced.