Shortcut to apply/remove strikethrough:

Keyboard shortcuts are essential for efficient navigation and formatting in various software applications, including word processors and spreadsheets. The question asks for the shortcut to apply or remove strikethrough formatting.

• The correct answer is Ctrl + 5. This shortcut toggles the strikethrough effect on selected text, drawing a line through the middle of the characters. It's a quick way to mark text as deleted or outdated without actually removing it.
• Ctrl + 4 is incorrect; it is commonly used to apply or remove underlining to text.
• Ctrl + 2 is incorrect; this shortcut is typically used to apply or remove bold formatting to text.
• Ctrl + 1 is incorrect; in many applications, like Microsoft Excel, it opens the 'Format Cells' dialog box, or in Word, it might change font formatting, but not specifically strikethrough.