 # Given below are two statements : One is labelled as Assertion A and the other `
Question:

Given below are two statements : One is labelled as Assertion A and the other labelled as reason $\mathrm{R}$

Assertion A : During the boiling of water having temporary hardness, $\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2}$ is converted to $\mathrm{MgCO}_{3}$.

Reason $\mathbf{R}$ : The solubility product of $\mathrm{Mg}(\mathrm{OH})_{2}$ is greater than that of $\mathrm{MgCO}_{3}$.

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

1. Both $A$ and $R$ are true but $R$ is not the correct explanation of $\mathrm{A}$

2. $\mathrm{A}$ is true but $\mathrm{R}$ is false

3. Both A and R are true and R is the correct explanation of $A$

4. $\mathrm{A}$ is false but $\mathrm{R}$ is true

Correct Option: , 4

Solution:

For temporary hardness,

$\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2} \stackrel{\text { heating }}{\longrightarrow} \mathrm{Mg}(\mathrm{OH})_{2} \downarrow+2 \mathrm{CO}_{2} \uparrow$

Assertion is false.

$\mathrm{MgCO}_{3}$ has high solubility product than $\mathrm{Mg}(\mathrm{OH})_{2}$.

According to data of NCERT table $7.9$ (Equilibrium chapter), the solubility product of magnesium carbonate is $3.5 \times 10^{-8}$ and solubility product of $\mathrm{Mg}(\mathrm{OH})_{2}$ is $1.8 \times 10^{-11}$. Hence Reason is incorrect.

The question should be Bonus.