Which action adds a slide number to every slide in the presentation?

Adding a slide number to every slide in a PowerPoint presentation is accomplished by accessing the appropriate options within the Insert tab. When you click on the Insert tab, selecting the slide number option enables you to specify that you want the slide number to appear on each slide. This involves checking the "Slide number" box in the Header and Footer dialog, which allows for consistency across all slides.

By using this method, the slide number is automatically populated on each slide, ensuring that the numbers are sequential and formatted uniformly throughout the entire presentation. This functionality is specifically designed to streamline the process of numbering slides, making it efficient and straightforward.

Other options do not specifically focus on inserting slide numbers for every slide. For example, footer options may include slide numbers, but they do not directly lead to the specific action of adding slide numbers to all slides in one step. Formatting slide numbers is not typically handled in the Design tab, where aesthetics are emphasized over content numbering. Additionally, the Review tab does not contain functions related to inserting slide numbers, which further clarifies why accessing the Insert tab is the correct approach for this task.