A cation or positively-charged ion containing arsenic, similar to how ammonium contains nitrogen.
From arsenic with the -onium suffix, which denotes cations or positive ions. This nomenclature mirrors ammonium and phosphonium ions.
The -onium suffix appeared in chemistry when scientists noticed patterns—ammonium, phosphonium, arsonium—and realized they could use the same ending to show 'this ion has gained a positive charge' across different elements.
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