Question

ASSERTION: Among alkali metal cations, $L{{i}^{+}}$ (aq) has the highest electrical conductance.
REASON: $L{{i}^{+}}$ (aq) is largest alkali metal cation because of greater degree of hydration
(a) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
(b) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
(c) Assertion is correct but Reason is correct
(d) Assertion is incorrect but Reason correct

Answer 1

Lithium is an alkali metal. Lithium is the smallest in size among the alkali metals. Hence $L{{i}^{+}}$ ion can polarize water molecules more easily than any other alkali metal.

Complete step by step solution:
In the anhydrous behavior of lithium because of its small size and the high nuclear charge i.e. the charge due to presence of nucleons in the nucleus. Lithium exerts the greatest polarizing effect out of all the alkali metals on the negative ion.
It is the dissolution of the substances in water by absorbing the water molecules by the weak valency forces. Smaller the cations greater will be the degree of hydration. Alkali metals easily use 1 electron therefore they have the value of oxidation potential which means that it has the high tendency to get oxidized. Hence it has a powerful reducing nature in the aqueous medium.
It is a fact that the lithium ion has the greatest reducing nature in aqueous medium due to the maximum hydration energy for the lithium ion. Greater the degree of hydration the mobility of the ions will be less, hence it will be less electrical conductance.

Hence the correct answer is option (D) i.e. Assertion is incorrect but Reason correct.

Note: It can also be understood by the surface charge density on which the magnitude of the hydration enthalpy depends. The surface charge is more for the smaller ions as they have higher force of attraction between the ion and the polar end of water.