Final answer:
Negative externality is when an exchange between a buyer and seller has a harmful impact on a third party. The existence of negative externalities justifies extra regulatory attention by financial institutions to minimize the harm caused to third parties.
Step-by-step explanation:
An externality occurs when an exchange between a buyer and seller has an impact on a third party who is not part of the exchange. It can have a negative or positive impact. A negative externality occurs when the impact is harmful to the third party, while a positive externality is when the impact is beneficial. In the case of negative externalities, like pollution from a power plant, the existence of these unintended harmful effects justifies extra regulatory attention by financial institutions to minimize the negative impact on third parties.