Give a brief account of the abundance of alkali metals and alkaline earth metals in the Earth's crust.

(N/A) Among the alkali metals,$Na$ and $K$ are abundant,while $Li$,$Rb$,and $Cs$ have much lower abundances.
$Fr$ is highly radioactive; its longest-lived isotope $^{223}Fr$ has a half-life of only $21 \ minutes$.
Of the alkaline earth metals,$Ca$ and $Mg$ rank fifth and sixth in abundance,respectively,in the Earth's crust.
$Sr$ and $Ba$ have much lower abundances.
$Be$ is rare,and $Ra$ is the rarest of all,comprising only $10^{-10} \ \%$ of igneous rocks.