Key concept: variation of molar conductivity with concentration

Molar conductivity $\Lambda_m$ behaves differently for strong and weak electrolytes.

• For a strong electrolyte, $\Lambda_m$ decreases gradually with concentration and follows approximately a linear relation of the type $\Lambda_m = \Lambda_m^0 - K\sqrt{C}$ (or in a plotted transformed variable, it gives a nearly straight-line trend).

• For a weak electrolyte, degree of ionization increases strongly on dilution, so $\Lambda_m$ rises sharply as concentration decreases. Hence its plot is highly curved, not linear.

Reading the graph qualitatively

In the given figure, one curve corresponds to a straight-line type decrease of $\Lambda_m$ with the concentration expression, while the other shows a curved variation.

Therefore:

• the straight-line plot corresponds to a strong electrolyte,
• the curved plot corresponds to a weak electrolyte.

Identification of A and B

From the graph:

• Electrolyte A shows the curved behavior $\Rightarrow$ weak electrolyte.
• Electrolyte B shows the linear behavior $\Rightarrow$ strong electrolyte.

Matching with options

This corresponds to: $\text{A = weak electrolyte, B = strong electrolyte}$

So the correct option is B.

Comparison with stored answer

Stored correct answer = B.

Our derived answer also = B.

Hence, they agree.