Question

The one which decreases with dilution is
A. Molar conductance
B. Conductance
C. Specific conductance
D. None of these

Answer 1

Hint: Specific conductance is measured by the conductance of unit volume of solution between the electrodes whereas molar conductance is measured for a constant concentration of solution. So the specific conductance depends on the concentration of the electrolytic solution.

Complete answer:
Conductance of any material is a property of a material quantifying its capacity to move electrons through itself. Now for electrolytic solution, we have free ions in the solution that move towards the electrodes, once it is connected across a closed circuit, and exchange electrons. Water in itself is not a good conductor but with salts in it, the dissociated ions make the salt solution conducting.
Specific conductivity is defined as the conductance of the solution existing between the two electrodes. The conductance will depend on the reactive area of the electrodes, and the concentration of the salts and therefore ions in the volume of solution. Let us assume that for different experiments with concentration of salts the area of the electrodes is constant. Then different concentrations of salt will have different specific conductance. It is therefore necessary to mention the concentration of salt when specifying conductance in terms of specific conductance.
Molar conductance is when one mole of salt is added to form the unit volume of solution. Molar conductance is defined for a constant concentration of salt and by definition is invariant with different concentrations. It is a more standard descriptor of conductance. Conductance on the other hand is a general purpose term and it is not mentioned without above mentioned qualifiers.
So, the correct answer is “Option C”.

Note: Molar conductivity is a more standard way to compare different electrolytes as by definition it is more restrained by the concentration of the salt, length, area of the electrodes and separation length between them. It can be understood in a way if we want to check conductivity of different metals, then we control the experiment by considering the same length, cross section area for different metals.