What are some of the potential obstacles that can lead to market failure by preventing a market from reaching the efficient outcome? Briefly define each obstacle

What will be an ideal response?

The obstacles basically fall into two camps: Obstacles that occur because the government does not intervene in the market and obstacles that occur because the government does intervene in the market. In the first group are the issues of externalities, public goods and common resources, and monopoly. An externality occurs when a cost or benefit from production falls upon someone other than the producer or when a cost or benefit from consumption falls upon someone other than the demander. A public good is a good or service that can be consumed simultaneously by everyone even if they didn't pay for the good or service. Public goods create the free rider problem, in which people consume the good without paying for it. A common resource is a resource that no one owns but everyone can use. A common resource is over-used. Finally, a monopoly occurs when a single producer controls the market by being the only producer. In the case of an externality, public good, or monopoly, government intervention has the possibility of increasing the market's efficiency.
The second set of obstacles occurs when a market is otherwise efficient but nonetheless the government intervenes in the market. The second group is comprised of price and quantity regulations, as well as taxes and subsidies. Some price regulations make prices higher than a certain price illegal; others make prices lower than a certain price illegal. Both prevent the market from reaching its (efficient) equilibrium. Taxes increase the price paid by the buyer and decrease the price received by the seller. Subsidies have the opposite effect, decreasing the price paid by the buyer and increasing the price received by the seller.
One last reason for a market to be inefficient that does not involve the government is high transactions costs. In this case it might be too expensive to operate a market.