Which of the following is correct?

Correct option is D

A firm reaches equilibrium when it maximizes profit or minimizes losses. This occurs where Marginal Revenue (MR) = Marginal Cost (MC).
· Perfect Competition: The equilibrium condition is MR = MC, not AR = MR (AR = MR only holds true under perfect competition, but equilibrium requires MR = MC).
· Monopoly: The firm maximizes profit where MR = MC, not where TR = MR.
· Monopolistic Competition: The equilibrium condition is also MR = MC, not AC = MC.
· Oligopoly: Firms under oligopoly follow the MR = MC rule for profit maximization.