Zend Certified PHP Engineer (ZCPE) Practice Test

To successfully delete a session variable in PHP, the appropriate method is to use the `unset()` function on that session variable. When you call `unset()` on a session variable, it effectively removes that specific variable from the `$_SESSION` superglobal array, which is used to manage session data in PHP.

The `unset()` function directly targets the variable and releases its reference, meaning the session will no longer hold any value for that variable. This ensures that subsequent access to the variable will return as if it had never been set, thus helping to manage the session state and memory cleanly.

While setting the variable to null might seem like it would clear the variable, it does not actually remove it from the session; instead, it simply assigns a null value to the variable, which still exists in the session. Therefore, it does not serve the purpose of completely deleting the variable.

The other options, such as trying to use a non-existent `delete()` function or a hypothetical `clear_session()` function, do not exist in the standard PHP session management functions, reinforcing that `unset()` is the correct method to delete a session variable effectively.