The yellow color of an aqueous solution of K2CrO4 changes to red-orange upon the addition of a few drops of HCl. The red-orange complex, the oxidation state of its central element(s), and the origin of its color, respectively, are:
1
chromium chloride, +3, d-d transition
2
dichromate ion, +6 and +6, charge transfer
3
perchlorate ion, +7, charge transfer
4
chromic acid, +6, charge transfer
5
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