Which statement best defines deadlock in a system with multiple processes?

• A. A set of processes are blocked waiting for each other.
• B. A program runs indefinitely due to an infinite loop.
• C. The system runs out of memory due to fragmentation.
• D. CPU scheduling prevents any process from making progress.

Answer: (A)

Deadlock happens when a group of processes becomes blocked because each one holds a resource and waits for another resource that is held by someone else in the same group. This creates a cycle of dependencies where no one can proceed because the resource it needs is held by a process that is itself waiting. For example, one process holds a resource and waits for another held by a second process, which waits for a resource held by the first or by another in the chain. Because everyone is waiting for someone else to release something, progress stops.

This specific situation describes the scenario where multiple processes are blocked waiting for each other, which is why it’s the correct definition of deadlock. The other scenarios describe different problems: an infinite loop is a single process stuck in repetitive execution, memory fragmentation is a memory management issue, and a scheduling problem that prevents progress from all processes could be a different kind of stall or even starvation, not the classic resource-wait cycle that defines deadlock.