The firm's profit-maximizing output occurs when:

The condition for a firm to maximize its profit occurs when marginal revenue equals marginal cost. This is a fundamental concept in microeconomics, particularly in the theory of the firm.

When a firm produces one additional unit of output, it considers both the additional revenue gained from selling that unit (marginal revenue) and the additional cost incurred to produce it (marginal cost). If marginal revenue exceeds marginal cost, the firm can increase its profit by producing more. Conversely, if marginal cost exceeds marginal revenue, the firm will reduce its profit by producing that extra unit.

Therefore, profit maximization is achieved precisely at the point where marginal revenue equals marginal cost. At this point, any further increase in production would lead to marginal costs surpassing marginal revenue, resulting in a decrease in profit, while producing less would mean the firm is not taking full advantage of its potential profit.

The other options do not accurately describe the profit-maximizing condition. For instance, total revenue maximization does not necessarily coincide with maximum profit, as a firm could generate high revenue but still operate at a loss if its costs are too high. Similarly, when average profit equals zero, the firm is at a break-even point, which is not indicative of profit maximization,