Half - cell reactions and Cell reactions

Electrochemical cell representation and half cell and cell reaction:
(I) Metal-Metal combination:

R : Anode  Zn → Zn²⁺ + 2e⁻
R : Cathode Cu²⁺ + 2e⁻ → Cu
Net Reaction Zn + Cu²⁺ → Zn²⁺ + Cu

R : Anode  (Cr → Cr³⁺ + 3e⁻) × 2
R : Cathode (Fe²⁺ + 2e⁻ → Fe) × 3
Net Reaction 2Cr + 3Fe²⁺ → 2Cr³⁺ + 3Fe
(II) Metal-H₂ combination:

R : Anode  Zn → Zn²⁺ + 2e⁻
R : Cathode 2H⁺ + 2e⁻ → H₂
Net Reaction Zn + 2H⁺ → Zn²⁺ + H₂

R : Anode  H₂ → 2H⁺ + 2e⁻
R : Cathode Cu²⁺ + 2e⁻ → Cu
Net Reaction H₂ + Cu²⁺ → 2H⁺ + Cu
(III) Metal Non-metal:

R : Anode  Mg → Mg²⁺ + 2e⁻
R : Cathode Cl₂ + 2e⁻ → 2Cl⁻
Net Reaction Mg + Cl₂ → Mg²⁺ + 2Cl⁻

R : Anode  2I⁻ → I₂ + 2e⁻
R : Cathode 2Ag⁺ + 2e⁻ → 2 Ag
Net Reaction 2I⁻ + 2Ag⁺ → I₂ + 2 Ag
(IV) Non-Metal, Non-Metal Combination:

R : Anode  2I⁻ → I₂ + 2e⁻
R : Cathode Cl₂ + 2e⁻ → 2Cl⁻
Net Reaction 2I⁻ + Cl₂ → I₂ + 2Cl⁻

Trick: In the representation of electrochemical cell we have to write Neutral to Neutral and left side oxidation always and right side reduction always.