Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The equivalent conductance of weak electrolyte falls off much more rapidly with increase in concentration. Reason (R): The equivalent conductance of weak electrolyte at infinite dilution can be determined by extrapolation of the curve between equivalent conductance vs $\sqrt{c}$ to zero concentration.}

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Strong electrolytes use extrapolation; Weak electrolytes need Kohlrausch's Law!

Answer 1

The Correct Option is C

Step 1: Concept The conductance of electrolytes depends on the number of ions and their mobility.

Step 2: Meaning Weak electrolytes dissociate partially. As concentration increases, the degree of dissociation ($\alpha$) decreases significantly, leading to fewer ions per unit volume.

Step 3: Analysis Assertion (A) is correct; the curve for weak electrolytes is very steep at low concentrations and falls rapidly as concentration increases. Reason (R) is incorrect because the curve for weak electrolytes becomes almost parallel to the y-axis at low concentrations, making it impossible to determine molar conductance at infinite dilution by extrapolation.

Step 4: Conclusion Only Kohlrausch's law can be used to find the value for weak electrolytes, not extrapolation. Final Answer: (C)