Question

Thermal stability of some salt is given. Which is correct?
A. $$L{i}_{2}C{O}_3<N{a}_{2}C{O}_3>K_{2}C{O}_3$$
B. $$L{i}_{2}O<N{a}_{2}O>K_{2}O$$
C. $$NaF<NaCl<NaI$$
D. $$BeS{O}_4>MgS{O}_4>CaS{O}_4$$

Answer 1

Hint: The stability is the stability of a liquid to withstand without the breakage in the presence of heat. The fluid or liquid can be heated at a high amount of temperature at which the liquid can be heated. And the stability of water can be described by using thermal stability. If a substance is thermally stable, that substance or material will not decompose at the presence of temperature.

Complete answer:
Here the given compounds are salts of alkali metal carbonates. And the size of the atom increases when down the group. Because the number of shells increases when the group. The order of thermal stability of metal carbonates are $$L{i}_{2}C{O}_3<N{a}_{2}C{O}_3>K_{2}C{O}_3$$.
Here, sodium carbonate has more thermal stability than potassium carbonate and lithium carbonate.
Thus, the thermal stability of the alkali metal carbonates increases when moving down the group. Because, the lattice energy is more in the case of similar size of anion and cation.
Hence, option (A) is correct.
Here the order of thermal stability of alkali metal oxide is not correct and the correct order is $$L{i}_{2}O>N{a}_{2}O>K_{2}O$$. Lithium oxide has more stability due to the size of metal oxide. Hence, the option (B) is incorrect.
In the case of $$NaF<NaCl<NaI$$, these are the ionic compounds and they are not in the correct order. Because, among these ionic compounds, sodium fluoride is more stable than sodium chloride and sodium iodide. Because thermal stability is related to the lattice energy. Here, the fluorine has smaller ionic size and there is a formation of stronger bonds. Hence, option (C) is incorrect.
In the case of $$BeS{O}_4>MgS{O}_4>CaS{O}_4$$, it is not in the correct order. And the correct order is $$BeS{O}_4<MgS{O}_4<CaS{O}_4$$. Here, calcium sulphate is more stable than that of magnesium sulphate and beryllium sulphate. Because, the thermal decomposition increases down the group. Hence, the option (D) is incorrect.

Hence, option (A) is correct.

Note:
We have to know that thermal stability mainly depends upon the size of the compounds. Because, the thermal stability is decreasing with increasing size. Which means, thermal stability is directly related with structure, size, bind angle, bond length etc. The stability decreases with increasing bond length. And it is also related with the electronegativity difference of the compounds.