Answer:
A) a situation in which the market on its own fails to allocate resources efficiently.
Step-by-step explanation:
A market failure happens when the total output of a good or service is less than or more than the socially optimal quantity.
In real life, a market is never able to achieve a socially optimal output, but coming close is generally good enough. When the price of a good or service is lower than the marginal social cost, then an over production and over consumption of the good will occur. On the other hand, when the price of a good or service is higher than the marginal social cost, then an under production and under consumption of the good will occur.
The greatest problems happen when there is an over provision of demerit goods, or private goods or services that are over consumed generating negative externalities.
The under production of merit goods is also a problem, since private goods that generate positive externalities aren't produced in enough quantities to satisfy the demand.
Marginal social cost = marginal private cost + marginal external costs (+ or -)