1. Additive inverse is the number you add to the given number in order to get 0. So -2/3.
2. Muiltiplicatice inverse of a/b is b/a. So 3/2.
3. x-y ≠ y-x. Just plug in numbers - 1-2≠2-1, 3-4≠4-3, etc...
4. Set of closed number is closed under addition and multiplication. Not subtraction because x-y can be negative, and negative numbers are not whole numbers (example: 3-5 = -2).
7. ab
8. ab/-1
9. No. Integers are closed under addition, subtraction, and multiplication. (Example: 8/6 is 4/3, which is not an integer.)