1. The shortcut key to open Task Manager in Windows is Ctrl + Shift + Esc.

2. This shortcut key is valid for Windows 10, Windows 11, and Windows 8.1.

3. Ctrl+Shift+Esc is a useful shortcut, specially created to quickly open the Task Manager.

System software is a program designed to run a computer's hardware and applications and manage its resources, such as its memory, processors, and devices. It also provides a platform for running application software, and system software is typically bundled with a computer's operating system.

Mail merge is a feature in Microsoft Word that allows you to create personalized documents, such as letters, envelopes, or labels, by combining a main document (containing generic content) with a data source (such as an Excel spreadsheet or a database) that contains specific information for individual recipients. This feature is commonly used for creating mass mailings or personalized communication materials.

The "@" symbol is used to separate the username of an email address from the domain name of the Internet Service Provider (ISP) or email service provider. For example, in the email address "username@example.com," "username" is the username of the email account, and "example.com" is the domain name of the email service provider, separated by the "@" symbol.

Parsing, in high-level language transformation, is the analysis of code syntax using formal grammar rules. It checks for errors and creates a parse tree representing the code's structure. This tree guides the generation of machine code or program execution, ensuring correct interpretation and execution of the source code.

In Windows, pressing the "Alt" key along with the "Tab" key (Alt+Tab) allows you to switch between open programs or applications. This keyboard shortcut displays a list of open windows, and you can cycle through them by continuing to press the "Tab" key while holding down the "Alt" key, and then release both keys to switch to the selected program.

All the mentioned errors are handled by OS. The OS is continuously monitoring all of its resources. Also, the OS is constantly detecting and correcting errors.