Statement I: The conductivity of solutions of both strong and weak electrolytes decreases on dilution.
Statement II: On dilution, the number of ions per unit volume of an electrolyte solution decreases.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I.
The conductivity (κ) of a solution is the conductance of one unit volume of it; the current in the solution is carried by its ions.
Statement I: The conductivity of solutions of both strong and weak electrolytes decreases on dilution. — True. Conductivity always decreases with decrease in concentration, whether the electrolyte is strong or weak.
Statement II: On dilution, the number of ions per unit volume of an electrolyte solution decreases. — True. Adding solvent spreads the ions through a larger volume, so fewer ions are present in each unit volume.
Why Statement II explains Statement I?
Conductivity measures the current carried by one unit volume of solution.
When dilution leaves fewer ions in that volume to carry the current, the conductivity falls, for strong and weak electrolytes alike.
NCERT (2026-27 edition):
2.4.2 Variation of Conductivity and Molar Conductivity with Concentration – “Both conductivity and molar conductivity change with the concentration of the electrolyte. Conductivity always decreases with decrease in concentration both, for weak and strong electrolytes. This can be explained by the fact that the number of ions per unit volume that carry the current in a solution decreases on dilution.”