if the expression is false, the_____ operator will return true.

negation

The operator that will return true if the expression is false is the logical NOT operator, represented by the exclamation mark (!) in most programming languages.

To use the logical NOT operator, you simply place it before the expression you want to evaluate. If the expression is true, the NOT operator will return false. If the expression is false, the NOT operator will return true.

Here's an example:

```python
x = 5
result = not x > 10
print(result)
```

In this example, the expression `x > 10` evaluates to false because 5 is not greater than 10. By applying the logical NOT operator (`not`) before the expression, it will return true. Therefore, the output will be `True`.