$(a)$ Give reactivity of alkaline earth metals towards air,water,dihydrogen and acids.
$(b)$ Explain reducing nature of alkaline earth metals.
$(c)$ Give chemical reaction of alkaline earth metals with liquid ammonia.

(N/A) $(i)$ Reactivity towards air and water: $Be$ and $Mg$ are kinetically inert to oxygen and water due to the formation of an oxide film on their surface. Powdered $Be$ burns in air to give $BeO$ and $Be_{3}N_{2}$. $Mg$ burns with dazzling brilliance to give $MgO$ and $Mg_{3}N_{2}$. $Ca$,$Sr$,and $Ba$ react readily with air to form oxides and nitrides,and react vigorously with water to form hydroxides.
$(ii)$ Reactivity towards dihydrogen: All elements except $Be$ combine with $H_{2}$ upon heating to form hydrides $(MH_{2})$. $BeH_{2}$ is prepared by the reaction: $2BeCl_{2} + LiAlH_{4} \rightarrow 2BeH_{2} + LiCl + AlCl_{3}$.
$(iii)$ Reactivity towards acids: Alkaline earth metals react with acids to liberate $H_{2}$ gas: $M + 2HCl \rightarrow MCl_{2} + H_{2}$.
$(iv)$ Reducing nature: Alkaline earth metals are strong reducing agents due to large negative reduction potentials,though less than alkali metals. $Be$ has a less negative reduction potential,but its reducing nature is attributed to high hydration energy of $Be^{2+}$ and high atomization enthalpy.
$(v)$ Liquid ammonia: They dissolve in liquid ammonia to form deep blue-black solutions: $M + (x+y)NH_{3} \rightarrow [M(NH_{3})_{x}]^{2+} + 2[e(NH_{3})_{y}]^{-}$.