The shortcut key used to center-align the selected text:

🧠 Explanation:

The shortcut key used to center-align the selected text in most word processing software, including MS Word, is **Ctrl + E**. This command quickly centers the text horizontally within the page or text box, improving the layout and visual appeal of the document. Using such shortcuts speeds up formatting tasks, allowing users to focus more on content creation. Mastering alignment shortcuts like Ctrl + E enhances productivity and helps produce professionally formatted documents with ease.