The prime number from the options provided is 89.
Here's the breakdown of the numbers:
- 89: Prime (Only divisible by 1 and 89)
- 81: Not prime (Divisible by 1, 3, 9, 27, 81)
- 87: Not prime (Divisible by 1, 3, 29, 87)
- 85: Not prime (Divisible by 1, 5, 17, 85)
Thus, 89 is the only prime number listed.