The reducing power of a metal depends on various factors. Suggest the factor which makes Li, the strongest reducing agent in aqueous solution.

Options

A. Sublimation enthalpy
B. Ionisation enthalpy
C. Hydration enthalpy
D. Electron-gain enthalpy

Answer

C

Explanation

Standard reduction potential `(E_(RP)^(@))` is a measure of tendency of an element to lose electron in aqueous solution. Higher the negative `E_(RP)^(@)` greater is the ability to lose electrons.
`E_(RP)^(@)` depends on
(i) enthalpy of sublimation
(ii) ionisation enthalpy
(iii) enthalpy of hydration
Thus, in aqueous medium, order of reactivity of alkali metals is `Na lt K lt Rb lt Cs lt Li. E_(RP)^(@)` value of Li is least `(-3.04V)` among all alkali metals.
The formation of `Li^(+)(aq)` from `Li` involves following steps
(i) `Li(s)overset("Sublimation")rarr Li(g)DeltaH_(s)=` Enthalpy of sublimation
(ii) `Li(g)rarr Li^(+)(s)" "IE_(1) =` ionisation enthalpy
(iii) `Li^(+)(g)rarr Li^(+)(aq)" "DeltaH_(n)=` Enthalpy of hydration
For alkali metals, enthalpies of sublimation are almost same. `IE_(1)` value of `Li` is endothermic and highest and hydration is exothermic and maximum for `Li^(+)`. The highly exothermic step (ii) for smallest `Li^(+)` makes it strongest reducing agent.