Which ion is represented by the formula dichromate?

The formula for the dichromate ion is indeed Cr2O7(2-). This ion consists of two chromium (Cr) atoms and seven oxygen (O) atoms, resulting in a total charge of -2. The dichromate ion typically forms when chromate ions (CrO4(2-)) undergo a protonation reaction in acidic conditions, leading to the formation of the dichromate species.

In chemical nomenclature, the "di" prefix in dichromate indicates that there are two chromium atoms present in the ion. Additionally, dichromate is often found in various chemical reactions and is an important species in redox chemistry, especially in titrations and environmental contexts involving chromium compounds.

The other choices represent different ions with distinct compositions and charges, which do not correspond to the dichromate ion. Thus, the representation of dichromate is accurately captured by the formula Cr2O7(2-).