An integer is a whole number that can be either positive, negative, or zero, while a whole number is a non-negative integer (0 and positive integers).
Given this, the options presented are:
- 25: This is a whole number and an integer.
- 2 fifths (2/5): This is a fraction, not an integer.
- 10: This is a whole number and an integer.
- -4: This is an integer but not a whole number (since it's negative).
- 3.5: This is a decimal, not an integer.
The only number that is an integer but NOT a whole number is -4.