what is the difference between negative and positive externalities
Externality Voluntary exchange is by definition mutually beneficial to both business parties involved, because the parties would not agree to undertake it if either thought it detrimental to their interests. However, a transaction can cause effects on third parties without their knowledge or consent. From the perspective of those affected, these effects may be negative (pollution from a nearby factory), or positive (honey bees kept for honey that also pollinate neighboring crops). Neoclassical welfare economics asserts that, under plausible conditions, the existence of externalities will result in outcomes that are not socially optimal. Those who suffer from external costs do so involuntarily, whereas those who enjoy external benefits do so at no cost.
Economic rent In economics, economic rent is any payment to an owner or factor of production in excess of the costs needed to bring that factor into production. In classical economics, economic rent is any payment made (including imputed value) or benefit received for non-produced inputs such as location (land) and for assets formed by creating official privilege over natural opportunities (e.g., patents). In the moral economy of neoclassical economics, economic rent includes income gained by labor or state beneficiaries of other "contrived" (assuming the market is natural, and does not come about by state and social contrivance) exclusivity, such as labor guilds and unofficial corruption.