Give reasons for the following:
(a). Alkanline earth metals cannot be obtained by chemical reduction.
(b). Alkaline earth metals have stronger tendancy to form complexes than alkai metals.
(c ). Magnesium nitride on reacting with water gives ammonia, but magnesium chloride does not give `HCI` on reacting with water.

Explanation

a. Alkaline earth metals cannot be obtained by chemical reduction, as they themselves are stronger reducing agents than common reducing agents. With carbon,they form carbides.
b. As compared to alkali metals, alkaline earth metal cation have
i. Smaller size,
ii. Greater charge
Hence, charge to radius ration or positive field of alkaline earth metals is greater, hence thery have greater tendency to form complexes.
c. Magnesium nitride, `Mg_(3)N_(2)`, is a salt of `Mg(OH)_(2)`, a strong base and `NH_(3)`, a weak acid, gets hydrolysed to give `NH_(3)`.
`Mg_(3)N_(2)+6H_(2)Orarr3Mg(OH)_(2)+2NH_(3)`
Whereas magnesium chloride, `MgCl_(2)`, is a salt of `Mg(OH)_(2)`, a strong base and `HCI`, a strong acid, hence it does not get hydrolysed.