To address this question, we need to identify which international organization signed a $500 million loan agreement with the Government of India on December 20, 2024, to support green and sustainable infrastructure projects. The options provided are:

• International Monetary Fund (IMF)
• Asian Development Bank (ADB)
• World Bank
• Asian Infrastructure Investment Bank (AIIB)

The correct answer is the Asian Development Bank (ADB).

Explanation:

• Asian Development Bank (ADB): ADB is a regional development bank established to promote social and economic development in Asia. It is known for providing financial support for infrastructure projects that include sustainability and green initiatives.
• International Monetary Fund (IMF): The IMF mainly focuses on macroeconomic stability and providing financial assistance to countries facing balance-of-payment problems. It is less likely to directly fund specific infrastructure projects.
• World Bank: While the World Bank also funds infrastructure projects, in this specific instance, it is the ADB that signed the loan agreement with India.
• Asian Infrastructure Investment Bank (AIIB): AIIB is another organization that focuses on infrastructure investment in Asia, but it is not the organization involved in this particular agreement with India.

Thus, based on the specific conditions and the organizations' roles, Asian Development Bank (ADB) aligns with the details given about the loan agreement to support green and sustainable infrastructure projects in India.