Question

The alkali metal which forms hydrate of chloride salt is:
A.Li
B.Na
C.Rb
D.Cs

Answer 1

Hint: Down the group the size of the elements increases while the polarizing power of alkali metal ions decreases. Lithium ions have the smallest size.

Complete step by step answer:
Among all alkali metal, lithium is smallest in size and this makes Li ion to have strongest polarizing power among all other alkali metal ions, so \[L{i^ + }\] ion helps in polarizing water molecules more easily than other alkali metals. This makes water molecules attach to lithium salt and form a crystal called water of crystallization. The salt crystalline hydrates which the other alkali metal chloride is unable to do. Polarizing tendency decreases down the group as the alkali metal becomes larger in size. Lithium ions are the smallest of them all. Lithium has a higher melting point so it reacts with water gently whereas other metals have lower melting point and react with water explosively. And also, other alkali metal forms anhydrous chloride. Sodium (Na), Rubidium (Rb), Cesium (Cs) are comparatively larger in size than Lithium and so have less polarizing power.
So, the alkali metal which forms hydrate of chloride is Lithium (Li).
 For Example: Li salt such as Lithium trihydrate lithium chloride (LiCl. \[3{H_2}O\] )
 Lithium dihydrate Lithium chloride (LiCl. \[2{H_2}O\] )

Therefore, the correct answer is option (A)

Note: Alkali metals are very reactive and they are found in nature in combined states with other elements. Lithium is soft, white and lustrous and many alloys and compounds of Li are produced on an industrial scale. It is the lightest metallic element.