Molar conductivity increases with.....
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Decrease in concentration
Molar conductivity is the conductivity per unit molar concentration, that is, the conducting power of all the ions from one mole of electrolyte:
\( \displaystyle \Lambda_m = \frac{\kappa}{c} \)
On dilution the conductivity \( \kappa \) falls, because there are fewer ions per unit volume. But the volume that contains one mole of electrolyte rises even more, so \( \Lambda_m \) increases as the concentration decreases. For a strong electrolyte the rise is slow and follows \( \Lambda_m = \Lambda_m^\circ - A\,c^{1/2} \); for a weak electrolyte it is steep at low concentration, because the degree of dissociation increases on dilution.
Why the other options are incorrect
Option (1) Increase in concentration — Incorrect. A more concentrated solution has a smaller molar conductivity: the ions are crowded, interionic attractions are stronger, and a weak electrolyte is less dissociated.
Option (2) Increase in pressure — Incorrect. Pressure hardly changes the volume, and so the concentration, of a liquid solution; molar conductivity is described as a function of concentration.
Option (4) Decrease in pressure — Incorrect. For the same reason, lowering the pressure does not raise the molar conductivity of a solution.
NCERT (2026-27 edition):
Variation of Conductivity and Molar Conductivity with Concentration – …
