Correct : b

The correct answer is Option B — First Come First Serve (FCFS) Scheduling.
A scheduling algorithm is preemptive if the CPU can be forcibly taken away from a running process before it completes. FCFS is the one algorithm in this list that cannot be preemptive — once a process gets the CPU, it holds it until it finishes or voluntarily blocks (e.g., for I/O). There is no mechanism by which a newly arriving process can displace the currently running one.
Option A — SRTF: Shortest Remaining Time First is the preemptive version of Shortest Job First by definition. When a new process arrives with a shorter burst time than the remaining time of the running process, the CPU is immediately preempted. It is always preemptive. Incorrect.
Option B — FCFS: Processes are scheduled strictly in arrival order and always run to completion. No preemption is possible under FCFS — not by design, and not by any variant of it. This is the only algorithm here that cannot be preemptive. Correct.
Option C — Round Robin: Built entirely around preemption — the time quantum is the preemption mechanism. When a process exhausts its time slice, the CPU is forcibly reassigned. Round Robin is always preemptive. Incorrect.
Option D — Priority Scheduling: Can be implemented in both modes. In the preemptive version, a higher-priority process arriving in the ready queue immediately preempts the current process. In the non-preemptive version, the CPU is only reassigned after the current process yields. Since it can be preemptive, it does not satisfy the question. Incorrect.
The key distinction: SRTF and Round Robin are defined by preemption and cannot operate without it. Priority Scheduling is flexible. FCFS is defined by non-preemption and cannot have preemption added without fundamentally changing its nature.