here is the answer.
Preempitive scheduling is the policy of scheduling that preempt the execution of current process and thread. And execute till such time its execution has completed or until a thread of a higher priority comes into existence or the priority of one of the waiting threads is increased.
Time Slicing is where each thread that is waiting to execute will share the CPU time equally. One thread will exeucte for n seconds or milliseconds, then go to the waiting state again. the CPU scheduler will then determine which of the other waiting threads will execute next.