Final answer:
When a blocked process completes its I/O service, it transitions to the Ready state, where it waits for CPU time to actually run.
Step-by-step explanation:
When a process in a computer system is in a Blocked state, this means it is waiting for an event or a resource, typically some form of I/O (Input/Output) service. Upon completion of the I/O service, the process transitions out of the blocked state. However, it does not immediately go into the Running state. Instead, it moves to the Ready state where it waits for the CPU scheduler to allocate it CPU time so that it can execute. Only when the scheduler selects it from the Ready state does it move into the Running state to execute its assigned tasks.