Question: there are four common oxyanions of chlorine?
Answer: For example, chlorine can combine with oxygen in four ways to form four different oxyanions: ClO4 − , ClO3 − , ClO2 − , and ClO − . (Note that in a family of oxyanions, the charge remains the same; only the number of oxygen atoms varies.) The most common of the chlorine oxyanions is chlorate, ClO3 − .