What is true about how a firm in a competitive market decides what level of output to produce in order to maxmize its profit?

In a competitive market, a firm maximizes its profit by producing the level of output where marginal cost (MC) equals marginal revenue (MR). At this point, the additional revenue generated from selling one more unit is exactly equal to the additional cost incurred in producing that unit. If the price is greater than the average total cost (ATC) at this output level, the firm earns a profit; if it's less, the firm incurs a loss. Therefore, the firm will adjust its output to reach this equilibrium where MC = MR.