To answer this question, you need to understand the LEN function in SQL.
The LEN function is used to return the number of characters in a specified string. In this case, the specified string is the variable @val, which is set to ' SQL is cool '.
The LEN function will count all characters in the string, including leading and trailing spaces. Therefore, the output of the query select LEN(@val) will be the total number of characters in the string, which is 12.
So, the correct answer is C) 12.