JEE Chemistry 2023 Question with Solution

Given: A graph of molar conductance $\Lambda_m$ versus concentration behavior for two electrolytes $A$ and $B$ is described. $\Lambda_m^\circ$ is the limiting molar conductivity.

Find: The number of incorrect statements.

For molar conductance, strong electrolytes show a linear dependence of $\Lambda_m$ on $\sqrt{C}$, whereas weak electrolytes show non-linear dependence because of incomplete ionization.

Electrolyte $A$ shows linear behavior, so its $\Lambda_m^\circ$ is obtained by extrapolation. Hence statement A is correct.

For electrolyte $B$, the $\sqrt{c}$ versus $\Lambda_m$ graph is not a straight line because $B$ behaves as a weak electrolyte. Hence statement B is incorrect.

At infinite dilution, the degree of dissociation of a weak electrolyte approaches unity, not zero. Hence statement C is incorrect.

By Kohlrausch's law, $\Lambda_m^\circ$ for an electrolyte can be calculated using $\lambda^\circ$ values for individual ions. Hence statement D is correct.

Therefore, the number of incorrect statements is $2$.

1. Statement A: For a strong electrolyte, $\Lambda_m$ varies linearly with $\sqrt{C}$, so $\Lambda_m^\circ$ can be obtained by extrapolation. This is correct.

2. Statement B: A straight-line relation between $\Lambda_m$ and $\sqrt{c}$ with intercept $\Lambda_m^\circ$ is valid for strong electrolytes, not weak electrolytes. So this is incorrect.

3. Statement C: For a weak electrolyte, degree of dissociation increases on dilution and approaches $1$ at infinite dilution. Therefore saying it approaches zero is incorrect.

4. Statement D: Using limiting ionic conductivities of individual ions, $\Lambda_m^\circ$ can be calculated. This is correct.

Thus, the incorrect statements are B and C, so the total number is $2$.

The solution contains some mismatched statement labels in its explanation, but the final correct answer concluded there is $2$ incorrect statements.