Which of the following function is used for determining missing values?

The correct answer is: C. is

The is function is used to determine if a value is missing. It returns a boolean value, TRUE if the value is missing and FALSE if the value is not missing.

The any function returns TRUE if any of the values in a list are true, and FALSE if all of the values in the list are false.

The all function returns TRUE if all of the values in a list are true, and FALSE if any of the values in the list are false.

Therefore, the is function is the only function that can be used to determine if a value is missing.