What is the primary purpose of the <em> tag in HTML?

The primary purpose of the <em> tag in HTML is to italicize text. This tag is semantically used to indicate emphasis of a word or phrase, which browsers typically render as italicized text to convey a different tone or importance.

Using the <em> tag not only alters the visual presentation of the text but also provides meaning for screen readers, which can announce the text as emphasized. This is an important aspect of accessibility in web development, as it allows all users, including those with disabilities, to understand the emphasis intended by the content creator.

While creating underlined text or bold text serves different purposes in HTML, the <em> tag specifically focuses on conveying emphasis through italicization. Additionally, list creation is handled using other HTML tags such as <ul>, <ol>, and <li>, which do not relate to the <em> tag's function. Thus, it is clear that the correct answer directly aligns with the tag’s intended use in HTML.