1.Describe Life cycle of Process

. New. The process is being created.

. Running. Instructions are being executed.

. Waiting. The process is waiting for some event to occur (such as an I/O

completion or reception of a signal).

. Ready. The process is waiting to be assigned to a processor.. Terminated. The process has finished execution.

2.why each process must have one PCB.

Process contorl block contains many pieces of information associated with a specific process,include process state,program counter,CPU registers,CPU scheduling information,memory management information,accounting information and I/O status information.
It is part of the process entity and is the most important recorded data structure in the operating system. It is the most important data structure for process management and control.