I think Q_Pheevr already clarified it in the quiz but HTML sub and sup tags will not work in the answer column, however unicode characters will. Unicode sub and superscripts only exist for a handful of common useful characters, whereas if they were available, HTML tags could be added to any text.
You can compare the difference between HTML and unicode sub and superscripts on this
wikipedia table. You'll notice straight away that the HTML versions look much better than the unicode equivalents.
Also try copying and pasting a unicode superscript and an equivalent HTML superscript into something like a Google search bar. You will see that the unicode version stays small, while the HTML version has the code stripped out so that it appears full sized. This is what happens when you attempt to use the HTML version in a Sporcle quiz.
A unicode ² is a distinct, separate character from 2. An HTML <sup>2</sup> is just an ordinary 2 character, which your browser has been told to raise and shrink.
If you want to use sub and superscripts in your quiz data, I'm afraid you're stuck with the rather more limited unicode versions, which can be copied and pasted from unicode sites or wikipedia. Unfortunately it is not always guaranteed that everyone will have these characters installed on their computers so some quiz players may complain that they are just seeing empty squares.