Option 1 -> Free movement of goods refers to trade without barriers, not uncompensated benefits or harms.
Option 2 -> Externalities are the costs or benefits affecting third parties who didn't choose to incur them, without compensation.
Option 3 -> Public goods are non-excludable and non-rivalrous goods like street lights, not about spillover effects.
Option 4 -> Environmental freedom is not a standard economic term for this concept.
Hence, Option 2: Externalities -> Externalities occur when economic activities create side effects on third parties without compensation. Negative externalities include pollution (harm without penalty), while positive externalities include vaccination (benefit without payment). This market failure happens because the full social costs or benefits aren't reflected in private transactions.-> correct