HTML - Superscript & Subscript In Slect Box

Hai
i am new to html. just now started learning html.i have a requirement like this.
In a select box i need to include formulas using super script and subscript.
if give like this
<select>
<option value="water">H₂0</option>
</select>
<sup> tag is not working?what can i do to display 2 as subscript.
it is simply displaying H20,what is the solution for this?


any ideas?

Thanks in advance


Regards
Indu