The oxidation state of the two elements can be looked up in the periodic table. The sum of the oxidation numbers in a compound must be zero. The crisscross method may be used numbers to determined the subscripts. mulas (3 Questions) \ 25. Which substance has a chemical formula with the same ratio of metal ions to nonmetal ions as in potassium sulfide? (1) sodium oxide (2) sodium chloride (3) magnesium oxide (4) magnesium chloride 2C-5 Naming Stock Compounds (13 Questions). Some metals have multiple common oxidation numbers. Compounds formed by these elements are distinguished by using Roman numerals after the metal that indicate the oxidation number. The proper oxidation number of the metal that ratios of the elements within the compound and their subscripts. The sum of the oxidation numbers in a compound must be zero. The crisscross method may be used. 27. Which formula correctly represents the composition of iron (III) oxide? (1) FeO3 (2) Fe₂O3 2C-6 Writing Stock 26, Write the formula for the salt barium chloride. [1] (3) Fe3O (4) Fe302 28. What is the correct formula for iron (III) phosphate? (1) FeP (3) FePO4 (2) Fe3P2 (4) Fe3(PO4)2 29. What is the formula of titanium(II) oxide? (1) TiO (3) Ti₂0 (2) TiO2 (4) Ti₂O3 written in Roman Numerals can be determined by using the 30. A compound is made up of iron and oxygen, only. The ratio of iron ions to oxide ions is 2:3 in this compound. The IUPAC name for this compound is (1) triiron dioxide (2) iron(II) oxide (3) iron(III) oxide (4) iron trioxide 31. What is the IUPAC name for the compound FeS? (1) iron (II) sulfate (3) iron (II) sulfide (2) iron(III) sulfate (4) iron(III) sulfide Formulas (4 Questions) Use the oxidation numbers to determined the subscripts. The oxidation state of the metal is given while the nonmetal can be looked up in the periodic table. The sum of the oxidation numbers in a compound must be zero. The crisscross method may be used 32. What is the chemical formula for tin(II) fluoride? [1] 33. Write the formula for arsenic (III) oxide. [1] 2C-7 Naming Polyatomic Compounds (4 Questions) The steps: If the polyatomic ion is negative, just name the positive ion first followed by the name of the polyatomic ion. If the polyatomic ion is positive, just name the polyatomic ion first followed by the negative ion with ending of -ide. If both the positive and negative ions are polyatomic, just name the positive polyatomic ion first followed by the negative polyatomic ion.