Consider the following compounds:
KO₂, H₂O₂ and H₂SO₄
The oxidation states of the underlined elements in them are, respectively,

CONCEPT:

Oxidation State

• The oxidation state (or oxidation number) of an element in a compound is the charge it would have if all bonds were ionic.
• Rules for determining oxidation states:
  • The oxidation state of an element in its standard form is 0 (e.g., O₂, H₂).
  • For monoatomic ions, the oxidation state is the same as the ion charge.
  • Oxygen usually has an oxidation state of -2, except in peroxides where it is -1 and in superoxides where it is -½.
  • Hydrogen usually has an oxidation state of +1 when bonded to non-metals and -1 when bonded to metals.
  • The sum of oxidation states in a neutral compound is 0, while in polyatomic ions it equals the ion charge.

EXPLANATION:

• In KO₂ (potassium superoxide):
  • Potassium (K) has an oxidation state of +1.
  • Oxygen in superoxide has an oxidation state of -½.
• In H₂O₂ (hydrogen peroxide):
  • Hydrogen (H) has an oxidation state of +1.
  • Oxygen in peroxide has an oxidation state of -1.
• In H₂SO₄ (sulfuric acid):
  • Hydrogen (H) has an oxidation state of +1.
  • Oxygen has an oxidation state of -2.
  • To balance the molecule:

    2(+1) + x + 4(-2) = 0
    ​x = +6

Therefore, sulfur (S) has an oxidation state of +6.

Therefore, the oxidation states of the underlined elements in KO₂, H₂O₂, and H₂SO₄ are respectively +1, -1, and +6.