code: def formula_html(self, reversed_=False):
          
          if self.H_count == 1:
              text = "H"
          elif self.H_count > 1:
              text = "H<sub>{}</sub>".format(self.H_count)
          else:
              text = ""
          seq = [self.symbol, text, self.charge_sign_html()]
          if reversed_:
              seq = reversed(seq)
          return "".join(seq)
docs: Chemical formula HTML
  
          Args:
              reversed (bool): reversed text for leftmost atom groups