If a market has no externalities, then marginal private cost:.....?

[Marcela M]

If a market has no externalities, then marginal private cost:..

A - exceed marginal social costs

B - equal marginal social costs

C - are below marginal social costs

D - intersect marginal social costs

[Crookedlettaman]

B--The equality of price with social marginal cost, by aligning the interest of the buyer with the interest of the community as a whole, is a necessary condition for economically efficient resource allocation.

[Maril]

B - because externalities occur when marginal private cost is either more or less than marginal social cost. When they are equal, there are no externalities.