I need help for ap chemistry ?

Question

What is CrO3 stand for. From my knowledge it is metal and non metal so bascailly it is Chromium (III) ? i dont know what to put for the O3. I know oxygen is diatomic

Answer 1

"For example, H2O is a covalent compound; if it were ionic, the hydrogens would be H^+ (oxidation number +1) and the oxygen would be O^2- (oxidation number -2)."

Since oxide is doubly-negative per oxygen atom, the three oxygen atoms make a total of six negative charges.  Since this is a compound, the overall charge is zero, so to balance the six negatives requires six positives.  The six positives can only comes from one source, the chromium, so it is Cr^6+.

So the compound is chromium (VI) oxide under IUPAC.  Old style names would include chromic oxide or chromium trioxide.