Match List-I with List-II.

List-I	List-II
A. $$Cd(s) + 2Ni(OH)_3(s) \to CdO(s) + 2Ni(OH)_2(s) + H_2O(l)$$	I. Primary battery
B. $$Zn(Hg) + HgO(s) \to ZnO(s) + Hg(l)$$	II. Discharging of secondary battery
C. $$2PbSO_4(s) + 2H_2O(l) \to Pb(s) + PbO_2(s) + 2H_2SO_4(aq)$$	III. Fuel cell
D. $$2H_2(g) + O_2(g) \to 2H_2O(l)$$	IV. Charging of secondary battery

We need to match each electrochemical reaction with the correct type of battery/cell.

A. $$Cd(s) + 2Ni(OH)_3(s) \to CdO(s) + 2Ni(OH)_2(s) + H_2O(l)$$

This is the Nickel-Cadmium (NiCd) cell discharge reaction. The NiCd cell is a secondary (rechargeable) battery, so this represents discharging of a secondary battery.

$$\Rightarrow$$ A matches with II

B. $$Zn(Hg) + HgO(s) \to ZnO(s) + Hg(l)$$

This is the reaction of a Mercury cell. Mercury cells are non-rechargeable, i.e., primary batteries.

$$\Rightarrow$$ B matches with I

C. $$2PbSO_4(s) + 2H_2O(l) \to Pb(s) + PbO_2(s) + 2H_2SO_4(aq)$$

In a lead-acid battery, during discharge: $$Pb + PbO_2 + 2H_2SO_4 \to 2PbSO_4 + 2H_2O$$. The given reaction is the reverse, which represents charging of the secondary battery.

$$\Rightarrow$$ C matches with IV

D. $$2H_2(g) + O_2(g) \to 2H_2O(l)$$

This is the reaction in a Hydrogen-Oxygen fuel cell.

$$\Rightarrow$$ D matches with III

The correct matching is: A-II, B-I, C-IV, D-III

Therefore, the correct answer is Option C.