Deadlock is a situation in which a set of processes are unable to proceed because each process is waiting for a resource that can only be released by another process in the set. In other words, deadlock occurs when there is a circular dependency between processes, where each process is waiting for a resource that is held by another process in the set.

The correct answer to the given question is option 'A': each process is blocked and will remain so forever. Let's understand why this is the correct answer in detail:

1. Deadlock Definition:
- Deadlock is a state where a set of processes are unable to proceed because each process is waiting for a resource held by another process in the set.
- Deadlock is characterized by mutual exclusion, hold and wait, no preemption, and circular wait.

2. Mutual Exclusion:
- Mutual exclusion means that only one process can access a resource at a time.
- If a process requests a resource that is currently being used by another process, it must wait until the resource is released.

3. Hold and Wait:
- Hold and wait means that a process holds at least one resource and is waiting to acquire additional resources that are currently held by other processes.
- This creates a circular dependency where each process is waiting for a resource held by another process.

4. No Preemption:
- No preemption means that a resource cannot be forcibly taken away from a process.
- A process can only release a resource voluntarily.

5. Circular Wait:
- Circular wait means that there is a circular chain of two or more processes, where each process is waiting for a resource held by another process in the chain.
- This circular dependency prevents any of the processes from progressing.

Based on the above characteristics of deadlock, option 'A' is the correct answer. In a deadlock situation, each process is blocked and will remain so forever because they are waiting for resources that are held by other processes in a circular chain. This prevents any of the processes from making progress, leading to a deadlock.