Question

Which metal bicarbonates do not exist in solid state:
i.$LiHC{{O}_{3}}$
ii.$Ca{{(HC{{O}_{3}})}_{2}}$
iii.$Zn{{(HC{{O}_{3}})}_{2}}$
iv.$NaHC{{O}_{3}}$
v.$AgHC{{O}_{3}}$
A.(i),(ii),(iii),(v)
B.(i),(ii),(iii)
C.(i),(ii),(v)
D.(ii),(iii),(iv)

Answer 1

Hint: Try to think about the properties of alkali and alkaline earth metals, especially about their electropositive nature. Lithium has some important and different characteristics from other elements in the group.

Complete answer:
Physical properties of alkali metals are: Alkali metals are silvery white in colour and are generally soft and light metals. Softness of alkali metals is because there is some weak metallic bonding in them attributed to the large size of the atoms. As we move down the group metallic bonding weakens and hence, softness increases. Potassium is softer than sodium. The densities of alkali metals are low and they also keep on increasing, progressing down the group. Potassium, however, is lighter than sodium. Lithium is the lightest metal which has a density of $0.534g/c{{m}^{3}}$. It cannot be stored in kerosene oil because due to low density of it, it floats on the surface. It is kept wrapped in paraffin wax. The low density of alkali metals is related to their large atomic size and weak metallic bond. However, going down the group, atomic size as well as atomic mass increases but the corresponding increase in atomic mass is not neutralised by the increase in atomic volume : Thus, the density gradually increases.
Alkali metals have low melting and boiling point. The low melting points are related to their larger atomic size, due to which the binding energies of their atoms in the crystal lattice are comparatively low. Further, when we move down the group, their atomic size increases and the metallic bond strength decreases which causes decrease in melting points. The boiling points of the members of this group also follow the same order for the above reason.
The metal bicarbonates (i) $LiHC{{O}_{3}}$ (ii) $Ca{{(HC{{O}_{3}})}_{2}}$ (iii) $Zn{{(HC{{O}_{3}})}_{2}}$ (v) $AgHC{{O}_{3}}$ does not exist in solid state. Anyways the metal bicarbonate (iv) $NaHC{{O}_{3}}$ exists in solid state. The alkali metals are highly electropositive in nature, these are the only elements in the periodic table which forms stable solid bicarbonates. However lithium because of its less electropositive nature, does not form solid bicarbonates.
So the correct option is c.

Note: Lithium shows properties which are very different from the other members of its group. This is due to the (i) exceptionally small size of the atom and ion and (ii) greater polarizing power of lithium ion (i.e., charge radius ratio). Due to these factors, there is increased covalent character of lithium compounds which is responsible for their solubility in organic solvents. Further, lithium shows diagonal relationship to magnesium.