Which number is blocked on the right-hand side of the AF Form 2100A series health record for a sponsor whose social security number is 987-65-4321?

The number blocked on the right-hand side of the AF Form 2100A series health record for a sponsor corresponds to the last digit of the sponsor’s social security number, which in this case is a key detail to consider. The social security number provided is 987-65-4321, and if we observe the last digit of this number, it is '1'.

In the context of the question, it is important to note that the AF Form 2100A uses the last digit of the social security number to determine which number is blocked. Since the last digit is '1', it indicates that the number that should be blocked on the right-hand side of the health record is indeed '1'.

This method helps in uniquely identifying and categorizing service members and their family members in the military health care system, establishing a straightforward reference point in their medical records. Therefore, the choice that accurately reflects the blocked number based on the provided social security number is '1'.