Question

Comprehension:
The elements of group 1 describe, more clearly than any other group of elements, the effects of increasing the size of atoms or ions on the physical and chemical properties. The chemical and physical properties of the elements are closely related to their electronic structures and sizes. These metals are highly electropositive and thus form very strong bases, and have quite stable oxo-salts. In the manufacturing of sodium hydroxide, chlorine and sodium carbonate, the sodium chloride is used as starting material.

Which is not correctly matched ?
$\left(1\right)\text{Basic strength of oxides}:C{s}_{2}O<R{b}_{2}O<N{a}_{2}O<L{i}_{2}O$
$\left(2\right)\text{Stability of peroxides}:N{a}_2{O}_2<K_2{O}_2<R{b}_2{O}_2<C{s}_2{O}_2$
$\left(3\right)\text{Stability of bicarbonates}:LiHC{O}_3<NaHC{O}_3<KHC{O}_3<RbHC{O}_3<CsHC{O}_3$
$\left(4\right)\text{Melting point}:NaF<NaCl<NaBr<NaI$

• A. 1 and 4
• B. 1 and 3
• C. 1 and 2
• D. 2 and 3

Answer 1

The correct option is A 1 and 4

(1) Basic strength of the oxides increase in the order $L{i}_{2}O<N{a}_{2}O<K_{2}O<R{b}_{2}O<C{s}_{2}O$. The increase in basic strength is due to the decrease in I.E. and increases in electropositive character.

(4) The melting points of the halides decrease in the order $NaF>NaCl>NaBr>NaI$, as the size of the halide ion increases. The decrease in melting point is due to increase in the covalent character with increase in the size of anion according to Fajan’s rule.

(2) Increased stability of the peroxide with increase in the size of metal ion is due to the stabilisation of large anion by larger cations as the lattice enthalpy increases.

(3) With increase in the size of the cation, the lattice enthalpy increases and the thermal stability increases.