Chromate is an ion that contains one chromium ion in its +6 oxidation state and 4 oxide atoms. Its overall charge is -2. Chromate ion is strongly oxidizing in acidic conditions, but weakly oxidizing in basic conditions. Chromates are generally bright yellow. They can be made by reaction of chromium(III) oxide and a metal oxide in a basic environment. The oxygen in the air boosts the chromium atom's oxidation state from +3 to +6.