Final answer:
Foreign aid can lead to a positive externality on the international scale by providing assistance that improves recipient countries' education and healthcare systems, contributing to overall well-being and social welfare.
Step-by-step explanation:
A positive externality on the international scale can arise from foreign aid. Foreign aid refers to the assistance provided by one country to another country in the form of money, resources, or other support. When countries provide foreign aid, it can lead to positive spillover effects on the recipient country's economy and society. For example, if a developed country provides financial aid to a developing country for the construction of schools or healthcare facilities, it can lead to an improvement in the recipient country's education and healthcare systems. This, in turn, can contribute to the overall well-being and social welfare of the country. Therefore, option 2: Foreign aid is the correct choice as it can lead to a positive externality on the international scale.