Figure 30.5 Chemical Oscillations. a) if X = predator and Y = prey, the densities of predators and preys keep on oscillating with time. X = IO3- and Y = I2 in the iodine clock reaction. b) When X is plotted versus Y, it shows a periodic behaviour. c) In special situations, all initial compositions lead to the same final cycle called the limit cycle. Three different initial paths leading to the limit cycle are shown.