Which formula represents potassium chromate?

Potassium chromate is represented by the chemical formula K2CrO4. This compound is composed of two potassium ions (K^+) for every chromate ion (CrO4^2-). The positive charge from the two potassium ions balances the negative charge from the chromate ion, ensuring the overall neutrality of the compound.

In the case of potassium chromate, the chromate ion itself contains one chromium atom surrounded by four oxygen atoms, and it carries a -2 charge. Therefore, two potassium ions are needed to balance this charge to create a stable compound. This structure is common in coordination compounds and highlights the chemistry of transition metals, where chromium in a +6 oxidation state is central to the chromate ion.

The other options provided represent different compounds. K2Cr2O7 is potassium dichromate, which contains a different ratio of chromium and oxygen. KCrO4 includes just one potassium ion and would have an imbalance of charges. K3CrO8 does not reflect the correct stoichiometry for common potassium chromate or any known stable compound in typical chemistry contexts. Thus, K2CrO4 is the accurate and correct representation of potassium chromate.