Answer: When a firm is operating in a perfectly competitive labor market: "the firm can buy as much or as little labor as it wants at a fixed, going wage rate."
Explanation:
1- "the wage the firm increases with the number of workers hired" - Is incorrect because The salary paid by the company is treated as a constant salary.
2- Correct.
3- "the firm’s marginal expense of labor (MEL) equals the cost of all workers hired." is incorrect because the firm’s marginal expense of labor (MEL) is equal to the salary (wage) rate.