Which elements are considered as alkaline earth metals? Give a brief description of them.

(N/A) The group-$2$ elements comprise beryllium $(Be)$, magnesium $(Mg)$, calcium $(Ca)$, strontium $(Sr)$, barium $(Ba)$, and radium $(Ra)$. They follow alkali metals in the periodic table.
These (except beryllium) are known as alkaline earth metals. The first element, beryllium, differs from the rest of the members and shows a diagonal relationship with aluminium.
Atomic and Physical Properties of the Alkaline Earth Metals:

Property	Beryllium $(Be)$	Magnesium $(Mg)$	Calcium $(Ca)$	Strontium $(Sr)$	Barium $(Ba)$	Radium $(Ra)$
Atomic number	$4$	$12$	$20$	$38$	$56$	$88$
Atomic mass $(g \ mol^{-1})$	$9.01$	$24.31$	$40.08$	$87.62$	$137.33$	$226.03$
Electronic configuration	$[He] \ 2s^{2}$	$[Ne] \ 3s^{2}$	$[Ar] \ 4s^{2}$	$[Kr] \ 5s^{2}$	$[Xe] \ 6s^{2}$	$[Rn] \ 7s^{2}$
Ionization enthalpy $(I)$ $(kJ \ mol^{-1})$	$899$	$737$	$590$	$549$	$503$	$509$
Ionization enthalpy $(II)$ $(kJ \ mol^{-1})$	$1757$	$1450$	$1145$	$1064$	$965$	$979$
Hydration enthalpy $(kJ \ mol^{-1})$	$-2494$	$-1921$	$-1577$	$-1443$	$-1305$	$-$
Metallic radius $(pm)$	$111$	$160$	$197$	$215$	$222$	$-$
Ionic radius $(M^{2+})$ $(pm)$	$31$	$72$	$100$	$118$	$135$	$148$
$m.p.$ $(K)$	$1560$	$924$	$1124$	$1062$	$1002$	$973$
$b.p.$ $(K)$	$2745$	$1363$	$1767$	$1655$	$2078$	$(1973)$
Density $(g \ cm^{-3})$	$1.84$	$1.74$	$1.55$	$2.63$	$3.59$	$(5.5)$
Standard potential $E^{\ominus}$ $(V)$ $(M^{2+} / M)$	$-1.97$	$-2.36$	$-2.84$	$-2.89$	$-2.92$	$-2.92$
Occurrence in lithosphere	$2^{*}$	$2.76^{**}$	$4.6^{**}$	$384^{*}$	$390^{*}$	$10^{-6 *}$

$^{*}$ ppm (part per million), $^{**}$ Percentage by weight