Alkali metal hydrides are strong reducing agents. Prove this statement.

Explanation

(i) All alkali metals react with hydrogen at about 673K (lithium at 1073K) to form the corresponding hydrides, which are ionic in nature.
(ii) Reactivity of alkali metals with hydrogen increases from Li to Cs.
`2M+H_2to2M^+H^-(M=Li,Na,K,Rb,Cs)`
(iii) Ionic character of the hydrides increases from Li to Cs
(iv) The decrease in ionization enthalpy down the group permits easy availability of electrons to hydrogen, forming `H^+` ion.
(v) The hydrides behave as strong reducing agents and their reducing nature increases down the group.