Which formula represents chromium(III) oxide?(1) CrO3 (3) Cr2O3 (2) Cr3O (4) Cr3O2

NY Regents Chemistry Exam Jan 2023

Which formula represents chromium(III) oxide? (1) CrO3

(2) Cr3O

(3) Cr2O3

(4) Cr3O2

Solution: Chromium oxide is an ionic compound because it is composed of a metal and a nonmetal. The charge of Cr is 3+ according to the roman numeral in the formula. The charge of O is -2 according to the Periodic Table. We cross multiply the numbers get the correct formula. Cr should get 2 from oxygen and O should get 3 from the chromium. We get Cr2O3, choice 3