Final answer:
In a monopsony market, the extra cost of hiring an additional unit of resource increases as the quantity of resource hired increases because the firm must raise wages for all workers as they hire more.
Step-by-step explanation:
In a monopsony market, the situation is similar to a monopoly, but instead of being the sole seller, the firm is the sole buyer of labor. When the company wishes to hire more workers, it must raise wages not only for the additional workers but also for all existing ones it could have employed at a previously lower wage. Consequently, the firm's extra cost of hiring an additional unit of resource, or the marginal cost of labor, increases as the quantity of resource hired increases.
This is due to the company facing the upward-sloping market supply curve of labor which makes the marginal cost of hiring additional labor greater than the wage paid to the last worker hired. The marginal cost curve therefore lies above the market supply curve for labor for any level of employment above the first worker.