Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason 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 R: The solubility product of $\mathrm{Mg(OH)}_{2}$ 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:

(C) $\mathbf{A}$ is true but $\mathbf{R}$ is false

(A) Both $\mathbf{A}$ and $\mathbf{R}$ are true and $\mathbf{R}$ is the correct explanation of $\mathbf{A}$

(B) $\mathbf{A}$ is false but $\mathbf{R}$ is true

(D) Both $\mathbf{A}$ and $\mathbf{R}$ are true but $\mathbf{R}$ is NOT the correct explanation of $\mathbf{A}$

JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Hydrogen

Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R:
Assertion A : During the boiling of water having temporary hardness,

Mg (HCO_{3})_{2}

is converted to

MgCO_{3}

.
Reason R: The solubility product of

Mg (OH)_{2}

is greater than that of

MgCO_{3}

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

(A)Both $A$ and $R$ are true and $R$ is the correct explanation of $A$
(B) $A$ is false but $R$ is true
(C) $A$ is true but $R$ is false✓ Correct
(D)Both $A$ and $R$ are true but $R$ is NOT the correct explanation of $A$

Answer: (C)

Solution

Temporary hardness due to

Mg (HC O_{3})_{2}

decomposes on boiling:

Mg (HC O_{3})_{2} Δ MgC O_{3} + H_{2} O + C O_{2}

, so the assertion is true. The reason is false: the solubility product of

Mg (OH)_{2}

(

\approx 5.6 \times 1 0^{- 12}

) is far smaller than that of

MgC O_{3}

(

\approx 6.8 \times 1 0^{- 6}

), not greater. Hence A is true but R is false.

JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Single correct option

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JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Hydrogen

Solution

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