Nora leaves leftover bread on her front lawn for pigeons to enjoy. Her neighbor Eva complains that the pigeons leave a mess on her property. What describes the given situation?

A third-party benefit refers to a situation where an individual or business's actions result in positive effects for individuals not involved in the transaction. In this case, while Nora may be providing food for the pigeons, the mess created does not benefit Eva; rather, it negatively affects her. Thus, this choice does not accurately describe the situation.

A positive externality occurs when an individual's actions confer benefits to others. Although Nora's intention is to feed the pigeons, the resulting mess does not provide any benefit to Eva; it only creates a nuisance. Therefore, this choice misrepresents the nature of the impact on Eva.

The free rider problem arises when individuals benefit from resources or services without paying for them, leading to under-provision of those goods. In this case, the issue is not about benefiting without compensation but rather about the adverse effects of Nora's actions on Eva. Hence, this choice does not apply to the situation.