Step 1: Think about what "equal share" really means.
When a question asks for equal share of CPU time, picture several processes waiting in a queue and imagine the CPU as a single resource being passed around fairly, like friends taking turns on a swing, each gets the same length of turn before passing it on.
Step 2: Test this picture against each algorithm.
FCFS just lets whoever arrives first hog the CPU till it finishes, so a long process can starve everyone else. Priority Scheduling favors high priority jobs, so low priority ones may wait indefinitely. Shortest Job Next always prefers the smallest job, so big jobs get pushed back repeatedly. None of these treat every process equally.
Step 3: See why Round Robin fits the picture exactly.
In Round Robin, every process is given a fixed time quantum, say $q$ milliseconds. Once its turn is over, whether the job is finished or not, it goes to the back of the ready queue and waits for its next turn. Over several rounds, every process gets exactly the same amount of CPU time per cycle, which is precisely the equal share the question is describing.
Step 4: Conclude.
Since only Round Robin guarantees this fair, cyclic distribution of CPU time among all processes,
\[ \boxed{\text{Round Robin}} \]