Which scheduling algorithm allots a fixed time slice to every process in rotation and is therefore used in time sharing systems?

The correct answer is C, Round Robin. In Round Robin scheduling every ready process is given the processor for a fixed period called the time quantum, and when that period expires the process is moved to the back of the queue and the next one is served. Because each user gets a turn within a short and predictable interval, the method is exactly what a time sharing operating system needs.

Option A, First Come First Served, serves processes strictly in the order in which they arrive, so one long job at the head of the queue makes everybody wait. Option B, Shortest Job First, picks the process with the smallest burst time, which gives the lowest average waiting time but starves long processes and needs the burst time to be known in advance. Option D, priority scheduling, selects the process with the highest priority and can starve low priority work altogether.