Consider the following statements. Identify the correct statements.
(A) The cell constant is usually determined by measuring the resistance of the cell containing a solution whose conductivity is already known.
(B) The SI unit of molar conductivity is S m2 mol-1.
(C) The conductivity of solutions of different electrolytes in the same solvent and at a given temperature differs due to charge and size of the ions in which they dissociate, the concentration of ions or ease with which the ions move under a potential gradient.
(D) The conductance of electricity by ions present in the solutions is called metallic conductance.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (C) only.
The conductance of an electrolytic solution is described by a few linked quantities:
Cell constant G* = l/A, where l is the distance between the electrodes and A their area. Since κ = G*/R, it can be found from the measured resistance: G* = κR.
Molar conductivity Λm = κ/c, the conductivity per mole of electrolyte.
Conduction in solutions is by the movement of ions; in metals it is by electrons.
(A) The cell constant is usually determined by measuring the resistance of the cell containing a solution whose conductivity is already known. — Correct. A KCl solution of known κ is placed in the cell, R is measured, and G* = κR.
(B) The SI unit of molar conductivity is S m2 mol-1. — Correct. With κ in S m−1 and c in mol m−3:
\( \displaystyle \Lambda_m=\frac{\kappa}{c}=\frac{\mathrm{S\,m^{-1}}}{\mathrm{mol\,m^{-3}}}=\mathrm{S\,m^{2}\,mol^{-1}} \)
(C) The conductivity of solutions of different electrolytes in the same solvent and at a given temperature differs due to charge and size of the ions in which they dissociate, the concentration of ions or ease with which the ions move under a potential gradient. — Correct. These are the factors that decide how much current the ions of an electrolyte can carry.
(D) The conductance of electricity by ions present in the solutions is called metallic conductance. — Incorrect. Conduction by ions is electrolytic (ionic) conductance; metallic (electronic) conductance is due to the movement of electrons in metals.
NCERT (2026-27 edition):
Measurement of the Conductivity of Ionic Solutions – “… The cell constant is usually determined by measuring the resistance of the cell containing a solution whose conductivity is already known. …”
“… ions in which they dissociate, the concentration of ions or ease with which the ions move under a potential gradient. … if κ is expressed in S m–1 and the concentration, c in mol m–3 then the units of Λm are in S m2 mol–1.”