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.
Point C in the image is called
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Limiting molar conductivity
Molar conductivity increases on dilution. The value it approaches as the concentration approaches zero is called the limiting molar conductivity, \( \Lambda^{\circ}_m \).
For a strong electrolyte, \( \Lambda_m \) plotted against \( c^{1/2} \) is a straight line:
\( \displaystyle \Lambda_m = \Lambda^{\circ}_m - A\,c^{1/2} \)
Extending this line to \( c = 0 \) gives the intercept on the \( \Lambda_m \) axis, which is \( \Lambda^{\circ}_m \). Point C marks this intercept, so it is the limiting molar conductivity.
Why the other options are incorrect
Option (1) Conductivity limit — Incorrect. There is no such term.
Option (2) Limited equivalent conductance at infinite dilution — Incorrect. Equivalent conductance is an older quantity defined per gram equivalent; the graph plots molar conductivity.
Option (3) Limiting conductance at infinite dilution — Incorrect. Conductance (G) belongs to a particular cell and solution; the intercept is a molar quantity, the conductivity per mole of electrolyte.
NCERT (2026-27 edition):
Variation of Conductivity and Molar Conductivity with Concentration – …
