Question

How many chromium-oxygen linkages exist in `Cr_2O_7^(2-)` ion?

Answer 1

I count...........4 such linkages..........

Explanation:

The normal representation of `"dichromate anion"` is as `""^(-)O(O=)_2Cr-O-Cr(=O)_2O^-`, and thus, with the oxygen bridge linking the 2 metal centres, each `Cr(VI+)` species is `"FOUR COORDINATE"`, and tetrahedral to a first approximation......

Chromate anion, `CrO_4^(-)` has the same formal oxidation state, but here no oxygen bridge. Solid salts of chromate anion are yellow, and dichromate salts are deep orange......

In aqueous solution these salts are in chemical equilibrium.......

#2CrO_4^(2−) + 2H^+ rightleftharpoons Cr_2O_7^(2−) + H_2O#