Comparing a known value with NULL results into . . . . . . . .

Answer: Option A

This question is about how MySQL handles comparisons with NULL values. NULL represents the absence of data, so comparing it to anything, even a known value, is tricky.
Here's why the answer is Option A: null:
In MySQL, comparing a value to NULL using standard comparison operators like =, <, >, <=, >=, or != always results in NULL. This is because MySQL doesn't consider NULL to be equal to anything, not even itself.

Example:
```sql SELECT 5 = NULL; -- Output: NULL ```
To check if a value is NULL, you need to use the IS NULL operator.
Example:
```sql SELECT 5 IS NULL; -- Output: 0 (false) ```
Therefore, the correct answer is Option A: null.