Identify electrolytes A and B from the graph behavior

In conductance plots:

• Strong electrolytes show a nearly linear decrease of molar conductance with $\sqrt{c}$.
• Weak electrolytes show a strongly curved plot, and their limiting molar conductivity $\Lambda_m^\circ$ is not obtained directly by extrapolation.

Hence from the usual graph shape:

• A = weak electrolyte
• B = strong electrolyte

Relevant facts

• For a strong electrolyte: $\Lambda_m = \Lambda_m^\circ - K\sqrt{c}$ So, $\Lambda_m$ vs $\sqrt{c}$ is a straight line with intercept $\Lambda_m^\circ$.

• For a weak electrolyte: $\alpha = \frac{\Lambda_m}{\Lambda_m^\circ}$ and as dilution approaches infinity, $\alpha \to 1$

• By Kohlrausch’s law of independent migration of ions, limiting molar conductivity can be calculated from ionic conductivities: $\Lambda_m^\circ = \nu_+ \lambda_+^\circ + \nu_- \lambda_-^\circ$ This applies to electrolytes in general, including weak electrolytes indirectly.

Check each statement

(A) $\Lambda_m^\circ$ for electrolyte A is obtained by extrapolation.

Since A is a weak electrolyte, its $\Lambda_m^\circ$ is not obtained reliably by direct extrapolation of $\Lambda_m$ vs $\sqrt{c}$.

So, (A) is incorrect.

(B) For electrolyte B, $\Lambda_m$ vs $\sqrt{c}$ graph is a straight line with intercept equal to $\Lambda_m^\circ$.

Since B is a strong electrolyte, this is correct.

So, (B) is correct.

(C) At infinite dilution, the value of degree of dissociation approaches zero for electrolyte B.

B is a strong electrolyte. At infinite dilution, dissociation is essentially complete, so degree of dissociation approaches 1, not $0$.

So, (C) is incorrect.

(D) $\Lambda_m^\circ$ for any electrolyte A and B can be calculated using $\lambda^\circ$ for individual ions.

This is true by Kohlrausch’s law.

So, (D) is correct.

Count incorrect statements

Incorrect statements are:

• (A)
• (C)

Therefore, the number of incorrect statements is $2$

Comparison with stored answer

Stored correct answer = $2$

Our derived answer matches the stored answer.