A process ID on Linux is a unique integer value that identifies a running process. The process ID can

range from 0 to a maximum limit, which is usually 32768 or higher, depending on the system

configuration. The process ID of 0 is reserved for the kernel’s idle task, and the process ID of 1 is

reserved for the init system, which is the first process launched by the kernel. The process IDs are

assigned sequentially to new processes, and are recycled when a process terminates. Therefore, the

only valid value for a process ID among the given options is 21398, which is an integer within the

possible range. The other values are not valid process IDs because they are either strings,

hexadecimal numbers, or file paths, which do not match the format of a process ID on

Linux. Reference:

Linux Essentials - Linux Professional Institute (LPI)

How Are Linux PIDs Generated? | Baeldung on Linux