Question

# Assertion: In electrolysis, the quantity of electricity needed for depositing 1 mole of silver is different from that required for 1 mole of copper.Reason: The molecular weight of silver and copper are different. A. Both assertion and reason are correct and the reason is the correct explanation of the assertion.B. Both assertion and reason are correct and the reason is not the correct explanation of the assertion.C. The assertion is correct but the reason is incorrect.D. Both assertion and reason are incorrect.

Hint: Electrolysis is a process in which the electric current is passed through a solution which consists of electrolytes such that the electrolytes with a positive charge move towards the negative electrode vice versa. Faraday's first law states that the mass of an element deposited at an electrode is directly proportional to the charge (Q).

-The given assertion is true because according to the first law of Faraday, the mass deposited is directly proportional to the charge in coulomb i.e.
\begin{align} & \text{m }\alpha \text{ Q} \\ & \text{Z = }\dfrac{m}{Q} \\ \end{align}
-Here, Z is the proportionality constant which is also known as Electro-chemical equivalent of the substance.
-Also, the given reason is correct because the molecular weight of both silver and copper are different i.e. 107 a.m.u. and 63 a.m.u. respectively.
-But the reason is not the correct explanation of the assertion because according to Faraday's first law, the quantity of electricity is different for the different mass of the atom but in the reason, the molecular weight of the atom is given.
-The reaction of the silver in the electrolysis process will be:
$\text{A}{{\text{g}}^{+}}\text{ + }{{\text{e}}^{-}}\text{ }\to \text{ Ag}$
- The reaction of the copper in the electrolysis process will be:
$\text{C}{{\text{u}}^{2+}}\text{ + 2}{{\text{e}}^{-}}\text{ }\to \text{ Cu}$
-Also, it is given in the question that one mole of silver and 2 moles of copper is taken. So, here the mass for silver will be 107g and for copper, the mass will be 126 by using the formula of no. of moles.
$\text{No}\text{. of moles = }\dfrac{\text{Mass}}{\text{Molar mass}}$
-For silver: $\text{1 = }\dfrac{\text{Mass}}{107}$ $\text{ Mass = 107g}$
- For copper: $\text{2 = }\dfrac{\text{Mass}}{63}$ $\text{ Mass = 126g}$
So, the correct answer is “Option B”.

Note: Faraday's second law states that the mass deposited or liberated (m) at the electrodes present in the solution is directly proportional to the equivalent weight € of the substance or atomic weight and inversely proportional to the valency i.e. $\text{m }\alpha \text{ E}$.