Which operator is used to check whether the expression is "NULL"?

Answer: Option A

This question is about finding out how to check if a value in MySQL is empty or missing. In other words, how do we tell if a field is NULL?

NULL means the value is empty, like a blank space.

Out of the options given:

Option A: IS NULL is the correct answer! It's used specifically to check if something is NULL.

Option B: NOT NULL is used when you want to make sure that a field *cannot* be empty.

Option C: ON is used in joins, which are a way to combine data from different tables.

Option D: None of the mentioned is wrong because IS NULL is the right answer.