What is the formula for dichromate ion?

The dichromate ion is represented by the formula Cr2O7(2-). This ion consists of two chromium atoms and seven oxygen atoms, which collectively carry a charge of 2-.

Dichromate ions are commonly encountered in various chemical reactions, particularly in redox reactions and in analytical chemistry due to their distinctive properties. The structure of dichromate includes two chromium atoms in different oxidation states, which allows it to participate in complex chemistry, including interconversions between dichromate and chromate ions, which have the formula CrO4(2-).

The other options represent different species or ions that do not correspond to the definition of dichromate. The choice CrO4(2-) corresponds to the chromate ion, which has a different chemical behavior and structure. CrO2(2-) and CrO3(2-) do not correspond to recognized ions and typically do not exist in stable forms under normal conditions. Thus, the formula for the dichromate ion is accurately represented by Cr2O7(2-), confirming it as the correct answer.