tribasic

Containing three univalent basic atoms or groups per molecule. Used of a base or salt. Na₃PO₄ is an example of a tribasic salt.

Triprotic.

In chem., having three hydrogen atoms replaceable by equivalents of a base: noting some acids.

Capable of neutralizing three molecules of a monacid base, or their equivalent; having three hydrogen atoms capable of replacement by basic elements on radicals; — said of certain acids; thus, citric acid is a tribasic acid.

containing three replaceable hydrogen atoms

having three atoms of a univalent metal