Which of the following statements is incorrect with respect to the pl…

The correct answer is Option (3) → For strong electrolytes, a straight line with positive slope is obtained

Molar conductivity Λ_m rises on dilution for every electrolyte, but in different ways. For a strong electrolyte it increases slowly and follows:

    \( \displaystyle \Lambda_m = \Lambda^\circ_m - A\,c^{1/2} \)

This is a straight line with intercept Λ°_m and slope −A, so Λ_m falls as the concentration rises. For a weak electrolyte the degree of dissociation increases sharply on dilution, so Λ_m rises steeply at low concentration and the plot is a curve.

• Option (1) For strong electrolytes, a straight line with an intercept equal to the limiting molar conductivity (Λ°_m) is obtained. — A correct statement about the plot. Extending the line to c^1/2 = 0 gives Λ°_m as the intercept.

• Option (2) For strong electrolytes, a straight line with negative slope is obtained — A correct statement about the plot. The slope is −A.

• Option (3) For strong electrolytes, a straight line with positive slope is obtained — The incorrect statement. The slope is −A, which is negative; a positive slope would mean Λ_m rises with concentration.

• Option (4) For weak electrolytes, a straight line is not obtained — A correct statement about the plot. Λ_m rises steeply near low concentration, so the plot is a curve and Λ°_m cannot be found by extrapolation.

NCERT (2026-27 edition):
Strong Electrolytes

Weak Electrolytes – “Weak electrolytes like acetic acid have lower degree of dissociation at higher concentrations and hence for such electrolytes, the change in Λ_m with dilution is due to increase in the degree of dissociation and consequently the number of ions in total volume of solution that contains 1 mol of electrolyte. In such cases Λ_m increases steeply (Fig. 2.6) on dilution, especially near lower concentrations. Therefore, Λ°_m cannot be obtained by extrapolation of Λ_m to zero concentration.”