In a perfectly competitive market, which condition must be met for a firm to achieve allocative efficiency?

In a perfectly competitive market, a firm achieves allocative efficiency when it produces the quantity of goods where the price equals the marginal cost of production. This means that the amount consumers are willing to pay for the last unit of the good is the same as the cost of making that unit. When this condition is met, resources are being used in the best way possible, as the benefits to consumers from the last unit produced exactly match the cost to the firm. For example, if a firm sells ice cream for $3 per cone and it costs $3 to make one more cone, then it is efficiently allocating resources because the price reflects the value to consumers. If the price were higher or lower than the marginal cost, it would mean that either too many or too few resources are being used for that product.