Answer : 2. "12"
Explanation :

1. There are a total of 12 function keys on the keyboard, labelled F1 to F12.

2. These keys usually perform a special function defined by the operating system or the currently running program.

- F1 key: It is used as a help key in almost every program. When this key is pressed a help screen opens.

- F2 key: In Microsoft Windows, renames a highlighted icon, file, or folder in all versions of Windows.

- F3 key: When on the Windows desktop, often opens a search feature for many programs, including Microsoft Windows.

- F4 key: Use to open or find a window in Windows 95 to XP.

- F5 key: In all modern Internet browsers, pressing F5 refreshes or reloads the page or document window.

- F6 key: Move the cursor to the address bar in Internet Explorer, Mozilla Firefox, and most other Internet browsers.

- F7 key: Commonly used to perform a grammar check in Microsoft programs, such as Microsoft Word, Outlook, etc.

- F8 key: It is used to enter the Windows Startup Menu.

- F9 key: Used to refresh the document in Microsoft Word.

- F10 key: In Microsoft Windows, activate the menu bar of an open application.

- F11 key: Used to enter and exit full-screen mode in all modern Internet browsers.

- F12 key: Use the Save As window in Microsoft Word.