(The reactant substance) has been oxidized / reduced to (the product substance).

The oxidation state of (the element) increased / decreased from (o.s. no.) in (the reactant substance) to (o.s. no.) in (the product substance).

Examples:

Explain whether the underlined substance has been oxidized or reduced, in terms of oxidation state.

1.   ZnO (s) + C (s) -> Zn (s) + CO (g)

Zinc oxide has been reduced to zinc.

The oxidatation state of zinc decreased from +2 in zinc oxide to 0 in zinc.

2. PbS (s) + 4H₂O₂ (aq) -> PbSO₄ (s) + 4H₂O (l)

Lead(II) sulfide has been oxidized to lead(II) sulfate.

The oxidation state of sulfur increased from -2 in lead(II) sulfide to +6 in lead(II) sulfate.

3. PbO (s) + H₂ (g) -> Pb (s) + H₂O (g)

Lead(II) oxide has been reduced to lead.

The oxidation state of lead decreased from +2 in lead(II) oxide to 0 in lead.

4. 2FeCl₂ (aq) + Cl₂ (g) -> 2FeCl₃ (aq)

FeCl₂ has been oxidized to FeCl_3.

The oxidation state of iron increased from +2 in iron(II) chloride to +3 in iron(III) chloride.