(i) The emf of the standard hydrogen electrode is Zero volts.
Fe / Fe³⁺ Fe²⁺, H²_(atm)pt E = 0.771 V
E_measured = E_R- E_L
(ii) emf of SHE = 0
E_measured = 0.771V - 0 = 0.771V.
(iii) ∴ The other half cell connected is Standard Hydrogen Electrode (SHE).

This law can be stated as, "at constant temperature, the strength of the current flowing through a conductor is directly proportional to the potential difference and inversely proportional to the resistance of the conductor".
Thus, I = \(\frac{V}{R}\), V = RI, V = Volts, I = ampere R= ohms.

Other metals such as aluminium, copper and silver also undergo corrosion, but at a slower rate than iron. Let us consider the reduction of aluminium,
\({ Al }_{ (s) }\rightarrow { Al }_{ (aq) }^{ 3+ }+{ 3e }^{ - }\)
Al³⁺, which reacts with oxygen in air to form a protective coating of Al₂O₃. This coating act as a protective film for the inner surface. So, further corrosion is prevented.

Oxidation occurs at the anode
\({ Pb }_{ (s) }\rightarrow { Pb }_{ (aq) }^{ 2+ }+{ 2e }^{ - }\)
The Pb²⁺ions combine with \({ SO }_{ 4(aq) }^{2-}\) to from PbSO₄ precipitate.
\({ Pb }_{ (aq) }^{ 2+ }+{ SO }_{ 4(aq) }^{ 2- }\rightarrow { PbSO }_{ 4(s) }\)
Reduction occurs at the cathode
\({ PbO }_{ 2(s) }+{ 4H }_{ (aq) }^{ + }+{ 2e }^{ - }\rightarrow { Pb }_{ (aq) }^{ 2+ }+{ 2H }_{ 2 }O(l)\)
The Pb²⁺ ions also combine with \({ SO }_{ 4(aq) }^{2-}\) ions from sulphuric acid to form PbSO₄ precipitate.
\({ Pb }_{ (aq) }^{ 2+ }+{ SO }_{ 4(aq) }^{ -2 }\rightarrow { PbSO }_{ 4 }\)

The overall redox reaction in Leclanche cell is
\( \mathrm{Zn}_{(\mathrm{s})}+2 \mathrm{NH}_{4 \text { (aq) }}^{+}+2 \mathrm{MnO}_{2(\mathrm{~s})} \longrightarrow \mathrm{Zn}_{(\mathrm{aq})}^{2+}+\mathrm{MnO}_{2} \mathrm{O}_{3(\mathrm{~s})}+\mathrm{H}_{2} \mathrm{O}(l)+2 \mathrm{NH}_{3} \)
The ammonia produced at the cathode combines with Zn²⁺ to form a complex ion [Zn (NH₃)₄]²⁺_(aq). As the reaction proceeds the concentration of NH₃ will decrease and the aqueous NH₃ will increase which lead to the decrease in the emf of cell.