Which of the following is a common file extension for compressed files?

The common file extension for compressed files is .zip. This format is widely used for packaging multiple files or folders into a single file, reducing their overall size and making it easier to store, share, or transfer them. The .zip format supports compression algorithms which allow it to significantly decrease the file size, making it a popular choice for file storage and email attachments.

In contrast, the other options represent different types of files: .exe is an executable file, which contains a program or application; .html is a markup language file used for creating web pages; and .jpg is an image file format commonly used for digital photos. Thus, these extensions do not serve the purpose of indicating a compressed file.