Marginal revenue can become negative for A. both competitive and monopoly firms. B. monopoly firms but not for competitive firms. C. neither competitive nor monopoly firms. D. competitive firms but not for monopoly firms.

B. monopoly firms but not for competitive firms.

Explanation:

Marginal revenue can become negative for monopoly firms but not for competitive firms.

A monopolist’s marginal revenue is always less than or equal to the price  of the good.

Marginal revenue is the amount of revenue the firm receives for  each additional unit of output. It is the difference between total revenue – price  times quantity – at the new level of output and total revenue at the previous  output (one unit less).

Since the monopolist’s marginal cost curve lies below its demand curve.  When a monopoly increases amount sold, it has two effects on total revenue:

– the output effect: More output is sold, so Q is higher.

– the price effect: To sell more, the price must decrease, so P is lower.

For a competitive firm there is no price effect. The competitive firm can sell  all it wants at the given price.

So the marginal revenue on a monopolist's additional unit sold is lower than the price, because it gets less revenue for selling additional units.

Marginal revenue can become negative – that is, the total revenue decreases from one output level to the next.

d. the economy will face inflation.