Q.xi. Write the electrode reactions and net cell reaction in NICAD battery.

Two lead-based grids (Pb and PbO2) immersed in dilute sulphuric acid, discharging by both electrodes converting to $PbSO_4$.

Construction (diagram description): a lead storage cell/battery consists of a set of lead grid plates filled with spongy lead (Pb) forming the anode, alternating with lead grid plates filled with lead dioxide (PbO2) forming the cathode, both sets of plates immersed in an aqueous solution of dilute sulphuric acid (about 38% by mass, density ≈1.28 g/mL) contained in an acid-resistant battery casing. The plates are kept apart by separators to prevent short-circuiting while allowing ion flow through the electrolyte; external terminals connect to the positive (PbO2) and negative (Pb) plate groups. (Diagram: a rectangular cell casing containing two interleaved sets of vertical grid plates — one set labelled 'Pb (anode, −)', the other 'PbO2 (cathode, +)' — both submerged in electrolyte labelled 'dil. $H_2SO_4$', with terminals at the top.)

Discharge reactions:

Anode (oxidation): $Pb(s) + SO_4^{2-}(aq) \rightarrow PbSO_4(s) + 2e^-$

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