The International Development Association (IDA) is an affiliate of the World Bank, making option 3 the correct answer. The IDA was established in 1960 as a specialized agency within the World Bank Group to provide financial assistance, low-interest loans, and grants to the world`s poorest countries. These countries, often referred to as "developing countries," face significant challenges in terms of poverty, limited access to resources, and underdevelopment.

Option 1 is incorrect because the IDA is not a voluntary association of developing countries. Instead, it is a financial institution within the World Bank Group that operates with the support of donor countries.

Option 2 is also incorrect because the IDA is not a federation of international lending agencies. While it works closely with other organizations within the World Bank Group, it operates as a distinct entity.

Option 4 is incorrect as well because the IDA is not an organization of donor countries of the European Union. The IDA receives funding from a wide range of donor countries, not exclusively from the European Union.

In summary, the IDA is an affiliate of the World Bank and provides financial support to the world`s poorest countries.