Which of the following CSS rules would you use to make a paragraph element italic?

To make a paragraph element italicized in CSS, using the rule that specifies font-style: italic; is the correct approach. The font-style property is specifically designed to set the style of the font, and one of its valid values is italic. When this rule is applied to a paragraph element, it instructs the browser to render the text of that paragraph in an italicized format, which is commonly used for emphasis or to signify titles of works, among other stylistic purposes.

The other options are focused on different aspects of text formatting. For instance, setting font-style: normal; does not change the font to italic; rather, it ensures that the text displays in its normal style. Similarly, font-weight: bold; is used to make the text bold, impacting its weight but not its style. Lastly, text-decoration: underline; adds an underline to the text, which affects its appearance, but does not influence whether the text is italicized or not. Each of these choices serves a unique purpose in CSS, but for the intent of italicizing text, specifying font-style: italic; is the only appropriate solution.