1 <p>You need to use the tags you learned in the chapter on<a>text markup</a>. Follow the example and choose the appropriate text tags.</p>

2 <p>This additional version of the<a>challenge</a>is designed to reinforce your text markup skills.</p>

3 <p><strong>Solution</strong></p>

4 <p>The solution to the challenge will be available in a few minutes. Use it if you encounter difficulties. In the meantime, try to complete the challenge on your own.</p>

5 &lt;!DOCTYPE html&gt; &lt;html lang="en"&gt; &lt;head&gt; &lt;meta charset="UTF-8"&gt; &lt;title&gt;Chemical Formulas&lt;/title&gt; &lt;link rel="stylesheet" href="style.css"&gt; &lt;/head&gt; &lt;body&gt; &lt;h1&gt;Chemical Formulas&lt;/h1&gt; &lt;p&gt;Chemistry studies chemical substances and their compounds. An example of such a formula is water - H&lt;sub&gt;2&lt;/sub&gt;O, where &lt;sub&gt;2&lt;/sub&gt; is the index showing the number of hydrogen atoms.&lt;/p&gt; &lt;p&gt;Carbon dioxide is also an example - CO&lt;sub&gt;2&lt;/sub&gt;. Indices in formulas are very important for the correct representation of chemical substances.&lt;/p&gt; &lt;ul&gt; &lt;li&gt;Water: &lt;ul&gt; &lt;li&gt;H&lt;sub&gt;2&lt;/sub&gt;O - water molecule&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;li&gt;Carbon dioxide: &lt;ul&gt; &lt;li&gt;CO&lt;sub&gt;2&lt;/sub&gt; - carbon dioxide molecule&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;li&gt;Salt: &lt;ul&gt; &lt;li&gt;NaCl - table salt&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;/ul&gt; &lt;ol&gt; &lt;li&gt;Chemical substances: &lt;ol&gt; &lt;li&gt;Water&lt;/li&gt; &lt;li&gt;Carbon dioxide&lt;/li&gt; &lt;li&gt;Salt&lt;/li&gt; &lt;/ol&gt; &lt;/li&gt; &lt;/ol&gt; &lt;/body&gt; &lt;/html&gt;