Final answer:
The answer explains which identifier is not a legal identifier in programming languages.
Step-by-step explanation:
The legal identifiers in programming languages have specific naming rules. The identifier 'outrageouslyAndShockinglyLongRunon' is a valid identifier because it follows the rules of using letters, digits, and underscores, but it is not recommended due to its length. However, the identifier '_42' is also valid because it starts with an underscore followed by a digit, which is allowed. The identifiers 'lovePotionNumber9' and '7thheaven' are also valid as they consist of letters and digits only.
Therefore, the answer is '
outrageouslyAndShockinglyLongRunon
'.