Question

The following compounds have been arranged in order of their increasing thermal stabilities. Identify the correct order.

(1)$K_{2}C{O}_3$ (2)$MgC{O}_3$ (3)$CaC{O}_3$ (4)$BeC{O}_3$

• A. $2<4<3<1$
• B. $4>2>3>1$
• C. $4<2<3<1$
• D. $2>4>3>1$

Answer 1

The correct option is C $4<2<3<1$

In all cases, for a particular set of e.g. Group 1 or Group 2 compounds, the thermal stability increases down the group as the ionic radius of the cation increases, and its polarising power decreases. Group 1 compounds tend to be more thermally stable than group 2 compounds because the cation has a smaller charge and a larger ionic radius, and so a lower polarising power. particularly when adjacent metals on the same period are compared.

$BeC{O}_3$ < $MgC{O}_3$ < $CaC{O}_3$ < $K_{2}C{O}_3$.

Hence,option C is correct.