Explain the action of hydrogen with alkali metals

Explanation

All alkali metals react with hydrogen at about 673K (lithium at 1073K) to form their hydrides, which are ionic in nature. Reactivity of alkali metals with hydrogen increases from Lito Cs
`2M + H_(2) to 2 M^(+)H^(-)`     (where M-Li, Na, K, Rb and Cs)