Conductivity of electrolytes is measured by using conductivity cell which contains two electrodes separated by a fixed distance \(‘l’\) and have an area of cross-section \(A\) The resistance R of conductivity cell is given by the relation

\[R = \frac{\rho l}{A} = \frac{l}{\kappa A}\]

The quantity \(l/A\) for a particular conductivity cell is constant denoted by \(G^*\) and is called cell constant. The cell constant can be determined by using a \(KCl\) solution whose conductivity is known accurately at various concentrations. The cell constant \(G^* = l / A = R\kappa\). The conductances of different solutions can be determine by using Wheatstone bridge principle.  The specific conductance of a solution k is given by

\[\kappa =\frac{G}{R}\]

The total conductance of the solution is the product of specific conductance and volume of the solution \(\kappa × V\). If the amount of electrolyte dissolved in solution is equal to the gram equivalent weight of the electrolyte, then the total conductance is known as equivalent conductance

\[\Lambda ­eq = 1000K /C\],

where C is the concentration of solution in gram equivalents per litre.

The unit of equivalent conductivity is ­\(\Omega^{−1}cm^2 eq^{−1}\) or \(Scm^2eq^{−1}\). If the amount of electrolyte dissolved in solution is equal to the gram molecular weight of electrolyte, then the total conductance is known as molar conductivity \((\Lambda_M)\).

The unit of molar conductivity is ­­\(\Omega^{−1}cm^2 mol^{−1}\). According to SI system, molar conductance is expressed

as \(S m^2 mol^{−1}\), if concentration is expressed in \(mol\text{ }m^3\). Specific conductance always decreases with the decrease in concentration both for strong and weak electrolytes due to the decrease in the number of ions per unit volume that carry the current in a solution.

The increase in equivalent conductance of a weak electrolyte solution with dilution is attributed to

both 1 and 2

The increase in equivalent conductance of a weak electrolyte solution with dilution is attributed to both increase in degree of dissociation and increase in ionic mobility. So the answer is (3).

Degree of dissociation is the fraction of the molecules in solution that are dissociated into ions. As the solution is diluted, the degree of dissociation increases. This is because the ions in solution are less likely to interact with each other, which allows more molecules to dissociate.

Ionic mobility is the speed at which an ion moves in solution. As the solution is diluted, the ionic mobility increases. This is because the ions are less likely to interact with each other, which allows them to move more freely.

The increase in both the degree of dissociation and ionic mobility leads to an increase in the equivalent conductance.

Option (1) is incorrect because only the increase in degree of dissociation is not sufficient to increase the equivalent conductance.

Option (2) is incorrect because only the increase in ionic mobility is not sufficient to increase the equivalent conductance.

Option (4) is incorrect because both the increase in degree of dissociation and ionic mobility contribute to the increase in equivalent conductance.