Conductivity of an electrolytic solution increases with increase in concentration. It is due to…
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → increase in the number of ions per unit volume that carry the current in a solution.
Conductivity (κ) is the conductance of a solution placed between two electrodes of unit area kept unit distance apart, i.e. of unit volume of the solution. In a solution the current is carried by ions, so κ depends on how many ions are present in that unit volume.
Higher concentration: more ions in each unit volume, so conductivity increases.
Dilution: fewer ions in each unit volume, so conductivity decreases (even though the molar conductivity increases).
So conductivity increases with concentration because of the increase in the number of ions per unit volume.
Why the other options are incorrect
Option (2) decrease in number of ions per unit volume that carry the current — Incorrect. This happens on dilution and lowers conductivity.
Option (3) increase in the resistance of the entire solution with the increase in the number of ions — Incorrect. More ions mean lower resistance, since conductivity is the reciprocal of resistivity.
Option (4) Increase in the degree of dissociation with increase in concentration of electrolyte — Incorrect. The degree of dissociation of a weak electrolyte decreases as concentration increases; it increases on dilution.
NCERT (2026-27 edition):
Variation of Conductivity and Molar Conductivity with Concentration – …
