Read the passage carefully and answer.
The molar conductivity of a solution at any given concentration is the conductance of the volume of solution containing one mole of electrolyte kept between two platinum electrodes with unit area of cross-section and at a distance of unit length. Both conductivity and molar conductivity change with the concentration of the electrolyte. Kohlrausch examined \( Ʌ°_m \) values for a number of strong electrolytes and observed certain regularities. He noted that the difference in \( Ʌ°_m \) of the electrolytes NaX and KX for any X is nearly constant. On the basis of the above observations, he enunciated the Kohlrausch law of independent migration of ions.
Units of conductivity and molar conductivity are, respectively
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(S/cm,\, S\, cm^2\, mol^{-1}\)
The units follow from the definitions. Conductivity, \( \kappa \), is the conductance of a column of solution of unit length and unit cross-section:
\( \displaystyle \kappa = G \times \frac{l}{A} \)
\( \displaystyle \text{unit of } \kappa = \mathrm{S} \times \frac{\mathrm{cm}}{\mathrm{cm^{2}}} = \mathrm{S\,cm^{-1}} \)
Molar conductivity is conductivity divided by the molar concentration (in mol cm−3):
\( \displaystyle \Lambda_m = \frac{\kappa}{c} \)
\( \displaystyle \text{unit of } \Lambda_m = \frac{\mathrm{S\,cm^{-1}}}{\mathrm{mol\,cm^{-3}}} = \mathrm{S\,cm^{2}\,mol^{-1}} \)
So the units are S/cm and S cm2 mol−1.
NCERT (2026-27 edition):
Conductance of Electrolytic Solutions – “… The SI units of conductivity are S m–1 but quite often, κ is expressed in S cm–1.”
Measurement of the Conductivity of Ionic Solutions – “… If we use S cm–1 as the units for κ and mol cm–3, the units of concentration, then the units for Λm are S cm2 mol–1.”