Final answer:
The b) Guest User account holds the lowest rank and possesses the least privileges, with restrictions on software installation, system changes, and access to user data.
Step-by-step explanation:
The lowest-ranking user account with the least privileges is b) Guest User.
In most computer systems, a Guest User has the most limited access to the computer's resources and is typically intended for users who need temporary access to the system. This account type is often restricted from installing software, changing system settings, or accessing other user's private data. On the contrary, a Standard User has more privileges, such as the ability to install peripherals and run programs, but cannot make major changes to the system without an administrator's permission. The Administrator account has elevated privileges and can make changes that affect all users of the system, including installing software and changing security settings. Lastly, a Superuser, primarily found in Unix-based systems, has the highest level of access, with the ability to execute all commands and access all files.