a)

b) A is better for coating the surface of the iron because its E⁰  value is more negative.

Or
a) 
b) A device used for the production of electricity from energy released during the spontaneous chemical reaction and the use of electrical energy to bring about a chemical change. The reaction gets reversed /  It starts acting as an electrolytic cell & vice – verse.

(a) A lead storage battery is a secondary battery.

The following chemical equations take place in a lead storage battery.

: 
When a battery is charged, the reverse of all these reactions takes place.

Hence, on charging, PbSO_4(s) present at the anode and cathode is converted into Pb_(s) and PbO_2(s) respectively.
b) 
Or

(a) Quantity of electricity passed = (2A) x (3 x 60 x 60s) = 21600 C

Thus, 2F i.e. 2 x 96500 C deposit Hg = 1 mole 21600 C will deposit Hg

= 0.11 mole
Or

At anode:             Al (s)                  -->     Al³⁺ (aq) + 3e^-] x2

At cathode:          Ni²⁺ + 2e^{-               -->}   Ni(s)                ] x3

Cell reaction:     2Al(s) + 3Ni²⁺(aq) --->   2Al³⁺(aq)  + 3Ni (s)

Applying nernst equation to the above cell reaction 

Kohlrausch's law of independent migration of ions: It states that the limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of its anion and cation.

A conductivity of a solution decreases with dilution because it leads to decrease in a number of ions per unit volume.