Final answer:
Synonyms of 'mandatory', 'obligatory', 'required', and 'requisite' include terms such as 'compulsory', 'essential', 'imperative', and 'necessary'. The options provided in the question are actually antonyms. Proper understanding of these terms is important for clear communication.
Step-by-step explanation:
The synonyms for mandatory, obligatory, required, and requisite all have to do with something that is necessary or compulsory, and the terms are often used interchangeably in contexts where a certain action or condition is imposed as a rule or is necessary for a particular outcome. Therefore, the options given: 'optional', 'unstipulated', and 'voluntary', are actually antonyms rather than synonyms of the aforementioned words.
Optional refers to something that is left to one's choice and is not compulsory. Unstipulated implies something that has not been specified or demanded as a formal term. Voluntary means done, made, or given willingly, without being forced or paid to do it.
To directly answer the question from the student, proper synonyms for the words mandatory, obligatory, required, and requisite could include terms like 'compulsory', 'essential', 'imperative', and 'necessary'.