I'm afraid you are getting things mixed up between the different question types that exist (in VLE's in general and specific to Moodle).
Multliple Choice Question type (MCQ)
The teacher can include almost anything in each of the choices. The student can only select one (or more, in the case of MCQ, Multiple Answers) of the possible choices or "answers" on offer.
The terminology for MCQ questions "answers" is not specific to Moodle.
In the Wikipedia article about MCQ, they say "respondents are asked to select the best possible answer (or answers) out of the choices from a list."
"Multiple choice items consist of a stem and a set of options."
"The options are the possible answers that the examinee can choose from, with the correct answer called the key and the incorrect answers called distractors."
For more info about the current Moodle terminology about question / answer / response / feedback, etc. see this discussion.
Short Answer question type (SA)
This is the type of question where you would like the student to be able to type a chemical formula. If you tell your students how to type the unicode superscript and subscript characters, then there is no problem for them to enter their answer as expected. You could even provide the needed characters in the text of your question for them to copy-paste (see attached example).
However, in the case of a far more complex formula such as
it is obviously quite impossible for the student to enter that into a SA answer box and even more impossible for the moodle quiz question engine to analyse that kind of answer.
"The student needs to be given comparable resources to the teacher. Otherwise the student will never be able to aspire to the standards a teacher thinks as normal."
In the light of my explanations above, I'm afraid I do not understand what you mean by that. The current impossibility for the student to enter complicated formula into a SA answer box is due the the inherent limitations of today's programing resources. This may change in the future, but it has nothing to do with "not providing comparable resources to teacher and student".