Typing chemical formula using markdown
<p>I'm writing some material using <em>Markdown</em> on <em>Mou</em>.<br>
And the chemical formula need to be used frequently.<br>
For example, I would typing </p>

<pre><code> H&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;        
</code></pre>

<p>Then, the sulfate acid can be represent as H<sub>2</sub>SO<sub>4</sub> .<br>
But I can't figure out how to represent the anion type formula in html.<br>
The figure shows like this:    </p>

<p><a href="https://i.stack.imgur.com/JUMhv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JUMhv.png" alt="enter image description here"></a></p>

<p>I try to typing       </p>

<pre><code> SO&lt;sub&gt;4&gt;&lt;sup&gt;2-&lt;/sup&gt;&lt;/sub&gt;   
</code></pre>

<p>It shows like this: SO<sub>4<sup>2-</sup></sub></p>