The Association of Southeast Asian Nations, commonly known as ASEAN, is a political and economic union of __________ in Southeast Asia.  

The correct answer is 10. The Association of Southeast Asian Nations (ASEAN) is a political and economic union of 10 member states in Southeast Asia: Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand, and Vietnam.

Why the Other Options Are Incorrect

• 2022: This is a year, not the number of member states.
• 2020: Also a year and unrelated to ASEAN membership.
• None of these: Incorrect because 10 is the correct answer.

Therefore, ASEAN is a union of 10 member states.