You're correct. If the mortgage payments are not required after the spouse's death, then it is not alimony. That was a trick question.

"Payments made under post-1984 agreements and decrees are classified as alimony only if the following conditions are satisfied:

1. The payments are in cash.

2. The agreement or decree does not specify that the payments are not alimony.

3. The payor and payee are not members of the same household at the time the payments are made.

4. There is no liability to make the payments for any period after the death of the payee."