<em>An integer is not negative if and only if it is not less than zero.</em>
Step-by-step explanation:
Observing each statement individually:
<em>An integer is negative if and only if it is not less than zero</em>
A number that is NOT less than 0 is greater than zero. Negative numbers are less than 0, so this is clearly incorrect.
<em>An integer is not negative if and only if it is less than zero.</em>
A number that is NOT negative is positive. Positive integers are integers greater than zero, so this is also incorrect.
<em>An integer is not negative if and only if it is not less than zero.</em>
A number that is NOT negative is positive. A number that is NOT less than zero is greater than zero, or positive. This statement is correct.
<em>An integer is less than zero if and only if it is not negative.</em>
A number that is less than zero is negative, and this statement claims that a number less is only less than zero if it is NOT negative. This is incorrect.
