Statement I: Lambda_m of a weak electrolyte shows a sharp increase wh…

The correct answer is Option (1) → Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

Molar conductivity, Λ_m, is the conductance of the volume of solution that contains 1 mol of the electrolyte. It rises when the number of ions coming from that 1 mol rises. A weak electrolyte such as acetic acid is only partly dissociated:

    \( \displaystyle \ce{CH3COOH <=> CH3COO^- + H^+} \)

Statement I: \( \Lambda_m \) of a weak electrolyte shows a sharp increase when the solution is diluted. — True. On dilution Λ_m of a weak electrolyte increases steeply, especially at low concentrations, unlike the small, gradual rise for a strong electrolyte.

Statement II: The degree of dissociation of a weak electrolyte increases with dilution of the solution. — True. A weak electrolyte has a lower degree of dissociation at higher concentration; diluting it shifts the equilibrium towards the ions, so α increases.

Why Statement II explains Statement I?

• Statement I is about how Λ_m changes with dilution; Statement II is about how much of the electrolyte breaks into ions.

• As α increases, the 1 mol of electrolyte gives many more ions, and that is why Λ_m rises so sharply. So Statement II is the cause of Statement I.

NCERT (2026-27 edition):
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.”

Fig. 2.6: Molar conductivity versus c½ for acetic acid (weak electrolyte) and potassium chloride (strong electrolyte) in aqueous solutions.