Which of the following is not a valid file format for saving PowerPoint presentations?

The answer is valid because .DOCX is a file format associated with Microsoft Word, not PowerPoint. PowerPoint presentations are typically saved in formats specifically designed for presentation slides, which include .PPTX, .POTX, and .PPTM.

The .PPTX format is the standard for regular PowerPoint presentations, while .POTX is used for saving presentation templates. The .PPTM format is similar to .PPTX but allows for macros, which are automated sequences that can streamline tasks in PowerPoint. Understanding this distinction is essential for ensuring that you use the correct file types for different Microsoft applications.