Answer: The correct answer is

Step-by-step explanation:
Chromate ion is formed by the combination of one chromium atom and four oxygen atoms. The ion formed has two more electrons.
An ion which has extra electrons carries a negative charge on them and the ion which has more electrons carries a positive charge on them.
As, chromate ions have 2 extra electrons, Thus, it carries a charge of -2.
Hence, the correct answer is
