sblock Elements 2 Question 13
13. The following compounds have been arranged in order of their increasing thermal stabilities. Identify the correct order.
$ \mathrm{K}_2 \mathrm{CO}_3 \text { (I), } \mathrm{MgCO}_3 \text { (II), } \mathrm{CaCO}_3 \text { (III), } \mathrm{BeCO}_3 \text { (IV) } $
$(1996,1 M)$
(a) I $<$ II $<$ III $<$ IV
(b) IV $<$ II $<$ III $<$ I
(c) IV $<$ II $<$ I $<$ III
(d) II $<$ IV $<$ III $<$ I
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Answer:
Correct Answer: 13. (b)
Solution: Thermal stability of salts with common anion depends on polarising power of cation. Greater the polarising power, lower be their thermal stability. Hence,
$$ \mathrm{BeCO}_3 \text { (IV) }<\mathrm{MgCO}_3 \text { (II) }<\mathrm{CaCO}_3 \text { (III) }<\mathrm{K}_2 \mathrm{CO}_3 \text { (I) } $$
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