# Given below are two statements:

Question:

Given below are two statements:

One is labelled as Assertion A and the other labelled as reason $\mathrm{R}$

Assertion $\mathbf{A}$ : 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 $A$

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 and $\mathrm{R}$ is also false

Correct Option: , 4

Solution:

For temporary hardness, $\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2} \stackrel{\text { heating }}{\rightarrow} \mathrm{Mg}(\mathrm{OH})_{2} \downarrow+2 \mathrm{CO}_{2} \uparrow$ 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.