Is it possible for perfect competitive market to be inefficient?

Answer 1

It is possible for perfectly competitive markets to be inefficient when externalities are present.

Externalities arise when an economic activity has an unintended impact on other economic agents and/or the market. This results in there being a socially optimal level of production that does not coincide with the privately determined equilibirum level of production derived from the supply and demand curves (which, respectively, represent the marginal private costs and marginal private benefits to producers and consumers).

With respect to the efficiency of markets, positive externalities result in too little of the good in question being produced. In this case, the market equilibrium is lower than desired (the marginal social benefit curve lies above the marginal private benefit [demand] curve). In this case, the efficient market outcome would occur where the marginal social beneift curve interests the marginal private cost (supply) curve.

When negative externalities occur, too much of the good in question is being produced. This results in the supply curve, which represents the marginal private costs of production, lying below the marginal social cost curve because the private cost curve fails to take into account the costs of production incurred by all of society. In this case, the efficient market outcome would occur where the marginal social cost curve coincides with the private marginal benefit (demand) curve.