Really fixed ions bolted on to the matrix of an ion exchanger. The active groups in the periodic table of elements must maintain a counter-ion of the opposite charge around itself. The most active (reactive) metals in the active groups are located near the lowermost left corner of the periodic table. For instance, sodium, lithium and potassium all highly reactive towards water, with group 1 (alkali metals, hydrogen) being the most reactive group in the periodic table.