What single command (no options or arguments) can be used to fully extract a file called abc.tar.bz2? )

gzip only handles the .gz (LZ77) compression format and cannot decompress bzip2-compressed data.

gunzip decompresses .gz files only and has no support for the bzip2 algorithm used in .bz2 files.

tar is a general-purpose archiving tool that supports multiple compression back-ends including bzip2. Modern tar implementations auto-detect the compression type from the file header, so tar with extraction flags handles both decompression and un-archiving of .tar.bz2 files in a single invocation. None of the other listed commands can process both the tar container and bzip2 compression together.

bz2unzip is not a standard Linux command and does not exist in common distributions.