Chromium form many different oxides that exhibit general acid-base behavior as well as displaying a range of different colors. Chromium (II) oxide, CrO, is basic. It is found in the form of an insoluble black powder. Chromium (III) oxide, Cr2O3 is the main oxide of chromium. It is amphoteric and while it is insoluble in water, it will dissolve in acid. It is used as a pigment, producing a dark green color. Chromium dioxide or chromium (IV) oxide, CrO2, in its natural state looks like black crystals. Chromium trioxide or chromium (VI) oxide, CrO3 is acidic oxide, or acidic anhydride of chromic acid. It will react with water to form chromic acid and will react with a base to form a chromium salt. In solid form, it is a dark red-orange granular complex. It is used in chrome-plating as a strong oxidizer, however, it is extremely toxic. The toxicity of chromium compounds depends on the oxidation state of the metal. Occupational exposure to chromium(VI) compounds has been associated with increased incidence of lung cancer. Chromium(III) is an essential nutrient that can be toxic in large doses. Major factors governing the toxicity of chromium compounds are oxidation state and solubility. Cr(VI) compounds, which are powerful oxidizing agents and thus tend to be irritating and corrosive, appear to be much more toxic systemically than Cr(III) compounds, given similar amounts and solubilities. Chromium (VI) oxide is the most toxic oxide from all chromium oxides that’s why it is very dangerous to throw away this product. So chromium trioxide is a hazardous waste.