Which command would uncompress a file named 'important.bz2'?

To uncompress a file named 'important.bz2', the command that should be used is 'bunzip2'. This command is specifically designed for decompressing files that have been compressed using the bzip2 program, which results in file extensions like .bz2. When 'bunzip2' is executed on a .bz2 file, it will decompress the file and remove the '.bz2' extension, leaving the original uncompressed file.

The other options provided do not serve the purpose of uncompressing a .bz2 file. Some of them are relevant to different compression formats; for instance, gzip, which is related to files ending in .gz, would not be applicable here. Similarly, the tar command you mentioned is typically used for extracting files from tar archives, which may be compressed with either gzip or bzip2 but would not directly apply to a standalone .bz2 file without first being bundled in a tar file.

Thus, 'bunzip2' is the correct tool for the job when dealing specifically with bzip2-compressed files.