a) NaBr + Cl₂ → NaCl + Br₂

Na+1Br−1 + Cl02 → Na+1Cl−1 + Br02

Br−1 → Br0 +1eCl0 +1e → Cl−1

1 × 1 × Br−1 → Br0 +1eCl0 +1e → Cl−1

⇒ Br−1 + Cl0 → Br0 + Cl−1

2NaBr + Cl₂ → 2NaCl + Br₂

b) Fe₂O₃ + CO → Fe + CO₂

Fe+32O−23 + C+2O−2 → Fe0 + C+4O−22

Fe+3 +3e → Fe0C+2 → C+4 +2e

2 × 3 × Fe+3 +3e → Fe0C+2 → C+4 +2e

⇒ 2Fe+3 + 3C+2 → 2Fe0 + 3C+4

Fe₂O₃ + 3CO → 2Fe + 3CO₂

c) CO + I₂O₅ → CO₂ + I₂

C+2O−2 + I+52O−25 → C+4O−22 + I02

C+2 → C+4 +2eI+5 +5e → I0

5 × 2 × C+2 → C+4 +2eI+5 +5e → I0

⇒ 5C+2 + 2I+5 → 5C+4 + 2I0

5CO + I₂O₅ → 5CO₂ + I₂

d) Cr(OH)₃ + Br₂ + OH^- → CrO₄^2- + Br^- + H₂O

Br0 +1e → Br−CrOH3+ 5OH−→ CrO42−+ 4H2O +3e

3 × 1 ×Br0 +1e → Br−CrOH3+ 5OH−→ CrO42−+ 4H2O +3e

⇒ CrOH3+ 3Br+ 5OH−→ CrO42−+ 3Br−+ 4H2O

2Cr(OH)₃ + 3Br₂ + 10OH^- → 2CrO₄^2- + 6Br^- + 8H₂O

e) H⁺ + MnO₄^- + HCOOH → Mn²⁺ + H₂O + CO₂

H++ MnO4−+ H+1C+2O−2O−2H+1 → Mn2++ H2O + C+4O−22

H+1C+2O−2O−2H+1 → C+4O−22 +2H+ +2e8H++ MnO4− + 5e→ Mn2++ 4H2O

5 × 2 × H+1C+2O−2O−2H+1 → C+4O−22 +2H+ +2e8H++ MnO4− + 5e→ Mn2++ 4H2O

⇒ 16H++ 2MnO4− + 5H+1C+2O−2O−2H+1 → 2Mn2++ 8H2O + 5 C+4O−22 +10H+

6H⁺ + 2MnO₄^- + 5HCOOH → 2Mn²⁺ + 8H₂O + 5CO₂

Nguyên tố Cl thể hiện bao nhiêu số oxi hóa