According to the Coase theorem, private parties can solve the problem of externalities if a. the cost of bargaining is small. b. the initial distribution of legal rights favors the person being adversely affected by the externality. c. the number of parties involved is sufficiently large. d. All of the above are correct.

A good has positive externality if the benefits to third parties not involved in production is greater than the cost. an example of an activity that generates positive externality is research and development. Due to the high cost of R & D, they are usually under-produced. Government can encourage the production of activities that generate positive externality by granting subsidies.

A good has negative externality if the costs to third parties not involved in production is greater than the benefits. an example of an activity that generates negative externality is pollution. Pollution can be generated at little or no cost, so they are usually overproduced. Government can discourage the production of activities that generate negative externality by taxation. Taxation increases the cost of production and therefore discourages overproduction. Tax levied on externality is known as Pigouvian tax.

Coase theorem has been proposed as a solution to externality. According to this theory, when there are conflicting property rights, bargaining between parties involved can lead to an efficient outcome only if the bargaining cost is low