(a) Why alkaline earth metals are harder, have higer melting ponts and higher densities than the alkali metals?
(b). Why the atoms of alkaline earth metals are smaller than the corresponding alkali metals?
(c ). Why alkaline earth metals have high electrical and thermal conductivities?
(d). What is black ash?
(e). Why the variation in physical properties of alkaline earth elements is not as regular as in the case of alkali metals?

Explanation

a. Alkaline earth metals have smaller size and stringer metallic bonding as compared to alkai metals, which results in closer packing in the metalic lattice. Consequently, alkaline earth metals are harder, have higher melting points and densities as compared to alkali metals.
b. Alkaline earth metals have smaller size and stronger metallic bonding as compared to alkali metals, lattice. consequently, alkaline earth metals are harder, have higher melting points and densities as compared to alkali metals.
c. Due to the presence of two loosely bound electrons in the valence electrons in the valance shell, which can freely move throughout the crystal lattice, alkaline earth metals have high thermal and electrical conductivities.
d. Black ash is a mixture of `Na_(2)CO_(3)` and `CaS`.
e. Since alkaline earth metals do not have the same crystal lattice structure, the variation in physical properties of alkaline earth elements is not as regular as in case of alkali metals.