Question

The correct increasing order of melting point of alkali metal carbonates is:
A) $C{s_2}C{O_3}$ $ < $ $N{a_2}C{O_3}$ $ < $ ${K_2}C{O_3}$ $ < $ $R{b_2}C{O_3}$ $ < $ $L{i_2}C{O_3}$
B) $L{i_2}C{O_3}$ $ < $ $N{a_2}C{O_3}$ $ < $${K_2}C{O_3}$ $ < $ $R{b_2}C{O_3}$ $ < $ $C{s_2}C{O_3}$
C) $L{i_2}C{O_3}$ $ < $ $R{b_2}C{O_3}$ $ < $ ${K_2}C{O_3}$ $ < $ $N{a_2}C{O_3}$ $ < $ $C{s_2}C{O_3}$
D) None of these

Answer 1

Hint In order to answer this question, you must recall the concept of chemical bonding where you have bond strength and order of melting and boiling point. Use the concepts of bond strengths of metals with carbonate compounds, and then by analyzing the correct logic select the correct option among the above given options.

Complete step by step answer:
Step 1: In this step, we will enlist the properties of melting point:
We know that the melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point, the solid and liquid phases exist in equilibrium.
And also, the melting point of carbonates of a particular group increases due to an increase in atomic size. This increases the Van der Waal attraction, which requires more heat to melt.
Step 2: In this step, we will enlist the melting point properties of the first group:
In the first group i.e. $Li,\,\,Na,\,\,K,\,\,Rb,\,\,Cs$ are IA group elements, and the melting point increases from $Li\,$to $Cs$.
Hence, the correct order of melting point of carbonates of the first group (IA) group elements is:
$L{i_2}C{O_3}$ $ < $ $N{a_2}C{O_3}$ $ < $${K_2}C{O_3}$ $ < $ $R{b_2}C{O_3}$ $ < $ $C{s_2}C{O_3}$

Therefore, option (B) is correct.

Note:The melting point of an element is basically the energy required to change the state of an element from its solid state to its liquid state. Which essentially implies breaking a few bonds. Thus, higher the stronger the bond between the atoms, higher will be the melting point. Let us look at the elements in the ascending order of their melting points.