The ions cr3+ and o2- combine to form the ionic compound chromium oxide. in what proportions do these ions combine to produce a neutral compound?
)a) 3: 2
)b) 3: 3
)c) 1: 1
)d) 2: 3
)e) 1: 3

To find the ratio of the the combination for the ion, write the charge of the cation as the subscript for the anion, and the charge of the anion as the subscript of the cation. This will make the charges effectively cancel and you will be left with a neutral ionic compound. Remember, that an ionic compound is made up of a metal and a nonmetal.
For Cr3+ and O2-, you will get the neutral compound to be Cr₂O₃.

The proportion these ions combine in is 2 to 3. 2 ions of Cr3+ and 3 ions of O2-

Your answer is D) 2:3