Hello Roberto,
The MULTICHOICE (MC) sub-question, as well as the MULTICHOICE_S (MCS) sub-question, of the Cloze question type rely on the <option> tag, where the answer is presented as a dropdown list of choices. There is no way to pass code with this tag because its permitted content is only "text, possibly with escaped characters". In other words, you cannot have equations with the MC or MCS questions.
However, you can have equations in the MULTICHOICE_V (MCV) and MULTICHOICE_H (MCH) sub-questions, as well as in the MULTICHOICE_VS (MCVS) and MULTICHOICE_HS (MCHS) sub-questions, where the answer is presented as a list of radio button choices. You can also have equations in the feedback of MCV, MCH, MCVS and MCHS questions. You can use LaTeX, MathML or AsciiMath.
With MCV, MCH, MCVS and MCHS questions, because { and } are used as delimiters by the Cloze question, if you're using LaTeX, you need to replace { with its HTML entity reference { and } with }. Also, most of the time, you will want to use \( and \) as delimiters for display within text, not on its own line with \[ and \] and not the older delimiters $$ and $$.
Here is an example:
https://moodleformulas.org/course/view.php?id=89§ion=15 ↗