Which of the following is the correct chemical formula for the chromate ion?

• A. CrO_3^{-}
• B. CrO_2^{-}
• C. CrO_4^{2-}
• D. Cr_2O_7^{2-}

Answer: (C)

Verified step by step guidance

1. Understand that the chromate ion is a polyatomic ion containing chromium and oxygen atoms.
2. Recall the common oxidation states of chromium in its oxyanions and the typical formulas associated with chromate and dichromate ions.
3. Recognize that the chromate ion has the formula where one chromium atom is bonded to four oxygen atoms, carrying an overall charge of 2-.
4. Write the chemical formula for the chromate ion as \(\mathrm{CrO_4^{2-}}\) to reflect one chromium atom, four oxygen atoms, and a 2- charge.
5. Note that other options like \(\mathrm{CrO_3^{-}}\), \(\mathrm{CrO_2^{-}}\), and \(\mathrm{Cr_2O_7^{2-}}\) correspond to different species or ions, such as dichromate for \(\mathrm{Cr_2O_7^{2-}}\).