The -ate/-ite/per-/hypo- Oxyanion Naming Pattern
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Naming a series of related oxyanions means using -ate for the most common member, -ite for one fewer oxygen, and the prefixes per- and hypo- for one more or two fewer still.
Chlorine forms four oxyanions in this series: perchlorate, ClO4−, carries the most oxygen; chlorate, ClO3−, is the common reference point; chlorite, ClO2−, carries one fewer oxygen than chlorate; and hypochlorite, ClO−, carries the fewest. The same -ate/-ite pattern applies to sulfate and sulfite, or nitrate and nitrite, though the exact oxygen count each suffix represents is not consistent from one element's series to the next.
Assuming "-ate always means four oxygens" because chlorate's series works that way fails immediately on sulfate, SO4 2−, or nitrate, NO3−, whose series carry different oxygen counts under the same suffix.