Assertion (A): In group III, Mg^2+ is not precipitated although Mg(OH)2 is only sparingly soluble. Reason (R): NH4Cl lowers [OH^-] so that the ionic product of Mg(OH)2 stays below its K_sp.

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is not the correct explanation of A

JEE Main levelSingle correct optionDifficulty 2 of 3qc071

Assertion (A): In group III, $Mg X^{2 +}$ is not precipitated although $Mg (OH) X_{2}$ is only sparingly soluble. Reason (R): $NH X_{4} Cl$ lowers $[OH X^{-}]$ so that the ionic product of $Mg (OH) X_{2}$ stays below its $K_{s p}$ .

With excess

NH X_{4} X^{+}

from

NH X_{4} Cl

the ionisation of

NH X_{3}

is repressed and

[OH X^{-}]

is small. The ionic product

[Mg X^{2 +}] [OH X^{-}]^{2}

then stays below

K_{s p}

Mg (OH) X_{2}

, so Mg stays in solution. Hence A and R are true and R explains A.