Which of these integers cannot be expressed as the difference of two squares? 5 7 8 9 10

The integer that cannot be expressed as the difference of two squares is 8.

Here's why:

1. 5 can be expressed as 3^2 - 2^2 = 9 - 4 = 5
2. 7 can be expressed as 4^2 - 3^2 = 16 - 9 = 7
3. 8 cannot be expressed as the difference of two squares. There are no two perfect squares that subtract to give 8.
4. 9 can be expressed as 5^2 - 4^2 = 25 - 16 = 9
5. 10 can be expressed as 6^2 - 4^2 = 36 - 26 = 10

So, the answer is 8.