Two solutions 'A' and 'B' are taken and diluted. On dilution, it was seen that the molar conductivity of 'B' increases to a smaller extent while that of 'A' increases to a much larger extent comparatively, which of the two is a strong electrolyte?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → B
Molar conductivity (Λm) increases on dilution for every electrolyte, but for different reasons:
Strong electrolyte (KCl, NaCl): it is already completely dissociated. Dilution only weakens the interionic attractions, so Λm increases slowly, following \( \Lambda_m = \Lambda_m^\circ - A\sqrt{c} \).
Weak electrolyte (\( \ce{CH3COOH} \)): it is only slightly dissociated at higher concentration. Dilution increases its degree of dissociation, the number of ions rises, and Λm increases steeply, especially near infinite dilution.
Solution B shows a small increase, so B is the strong electrolyte; A, with a much larger increase, is a weak electrolyte.
Why the other options are incorrect
Option (2) A — Incorrect. A steep rise of Λm on dilution is the behaviour of a weak electrolyte.
Option (3) A and B both will be a strong electrolyte — Incorrect. Two strong electrolytes would both show a small, gradual increase; A and B behave differently.
Option (4) A and B both will be weak electrolyte — Incorrect. B’s small increase does not fit a weak electrolyte, whose dissociation grows a lot on dilution.
NCERT (2026-27 edition):
Summary – “… Conductivity decreases but molar conductivity increases with decrease in concentration. It increases slowly with decrease in concentration for strong electrolytes while the increase is very steep for weak electrolytes in very dilute solutions.”