Question

Given below are two statements : One is labelled as Assertion A and the other labelled as reason R.
Assertion A : During the boiling of water having temporary hardness, $Mg(HC{O}_3{)}_2$ is converted to $MgC{O}_3$.
Reason R : The solubility product of $Mg(OH{)}_2$ is greater than that of $MgC{O}_3$.

In the light of the above statements, choose the most appropriate answer from the options given below :

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• A. Both A and R are true but R is not the correct explanation of A
• B. Both A and B are false
• C. A is true but R is false
• D. Both A and R are true and R is the correct explanation of A

Answer 1

The correct option is B Both A and B are false

Boiling of temporary hardness water,
$Mg\left(HC{O}_3{)}_2\stackrel{Heating}{\to }Mg\right(OH{)}_2\downarrow +2C{O}_2\uparrow$
Thus, Assertion is false.

$Mg(OH{)}_2$ is less soluble than $MgC{O}_3$. On boiling temporary hard water containing $M{g}^{2+}$ ions, the precipitate obtained is of $Mg(OH{)}_2$ and not that of $MgC{O}_3$.
Hence, solubility product of $MgC{O}_3$ is greater than that of $Mg(OH{)}_2$.
Thus, both assertion and reason are false.

Hence, option (d) is correct.