• Transition metals?are characterized by having?variable oxidation numbers.
• Oxidation numbers?can be used in the names of compounds to indicate which?oxidation number?a particular element in the compound is in
• Where the element has a?variable oxidation number, the number is written afterwards in?Roman numerals.
• This is called the?STOCK NOTATION?(after the German inorganic chemist Alfred Stock), but is not widely used for non-metals, so SO₂?is sulphur dioxide rather than sulphur(IV) oxide
• For example, iron can be both +2 and +3 so?Roman numerals?are used to distinguish between them
  • Fe²⁺?in FeO can be written as?iron(II) oxide
  • Fe³⁺?in Fe₂O₃?can be written as?iron(III) oxide

Answer:

Answer 1: copper(I) oxide:

The ox. no. of 1 O atom is -2 and Cu₂O has overall no charge so the ox. no. of Cu is +1

Answer 2:?manganese(II) sulfate:

The charge on the sulfate ion is -2, so the charge on Mn and ox. no. is +2

Answer 3: sodium chromate(VI):

The ox. no. of 2 Na atoms is +2 so CrO_4?has an overall -2 charge, so the ox. no. of Cr is +6

Answer 4:?potassium manganate(VII):

The ox. no. of a K atom is +1 so MnO_4?has overall -1 charge, so the ox. no. of Mn is +7

Answer 5: sodium dichromate(VI):

The ox. no. of 2 Na atoms is +2 so Cr₂O_7?has an overall -2 charge, so the ox. no. of Cr is +6. To distinguish it from CrO_4?we use the prefix di in front of the anion