Solution

The correct answer is 4) A, C and D Only

Key Points

• A. I/O request → Ready Queue? ❌ When a running process issues an I/O request, it becomes blocked for that I/O and moves to the Waiting/Blocked queue, not the Ready queue.
• B. Create subprocesses & wait ✅ A running process can fork/spawn subprocesses and then call a wait (e.g., wait()) to block until children terminate. This is a valid transition (Running → Waiting).
• C. Time slice expires → Waiting Queue? ❌ On time quantum expiry (preemption), the process is put back into the Ready queue, not the Waiting queue (since it isn’t waiting for any event/I/O).
• D. Interrupt arrival → Waiting Queue? ❌ An interrupt may preempt the running process, after which it normally goes to the Ready queue. It moves to the Waiting queue only if it explicitly blocks for an event/I/O.

Hence, the events that cannot occur as stated are A, C, and D.