Answer:
tax; marginal external cost
Step-by-step explanation:
Here are the options to this question :
tax; marginal external cost
subsidy; marginal social benefit
tax; marginal social benefit
subsidy; marginal external benefit
Externality is when the activities of economic agents affect third parties not involved in the economic activity.
Negative externality is when the benefits of economic activities to third parties is less than its cost.
An example of an activity that generates negative externality is pollution. The aim of government would be to reduce pollution. To do this, the government would tax the economic agent involved in the pollution an amount equal to the marginal external cost. Taxes increases cost of pollution to the party involved in causing the pollution and thus would act as an incentive for the firm to reduce pollution produced.
Postive externality is when the benefits of economic activities to third parties exceeds the costs.
Government can encourage the production of activities that generate positive externality by providing subsides at an amount equal to the marginal external benefit
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