Selenium Trioxide and Selenic Acid

Compounds of hexavalent selenium are much more easily reduced than analogous compounds of either hexavalent sulfur or hexavalent tellurium this trend is analogous to that in the scries C (V)—Br(V)—I(V) (p. 224). 

It should be noted that the common form of telluric acid, HcTeO , is not analogous to sulfuric and selenic acids but is more fully hydrated. The series of oxy-acids derived from the maximum valence state of the members of group VIb is thus formally similar to that derived from group Vb (H3PO4, H3ASO4, Sb(OH) ). 

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