Such a feat cannot be done without using VBA. You can only apply a
font change to the entire cell if it contains a formula. If the cell
is not a formula  then you can have different font styles for each
character.

So, for column  C the value would need to be static before you can
apply a subscript change to the 2nd character.

This routine would change the Active Cell as you want...

ActiveCell.Copy
ActiveCell.PasteSpecial Paste:=xlPasteValues
ActiveCell.Characters(2, 1).Font.Subscript = True

You could place this in a loop to change all of column C at one time.
Just one method...