Assertion (A): Mg^2+ is not precipitated by (NH4)2CO3 in presence of NH4Cl in group V. Reason (R): NH4+ lowers [CO3^2-] through NH4+ + CO3^2- NH3 + HCO3-, and MgCO3 is considerably more soluble than the group V carbonates, so its ionic product stays below 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 3qc208

Assertion (A): $Mg X^{2 +}$ is not precipitated by $(NH X_{4}) X_{2} CO X_{3}$ in presence of $NH X_{4} Cl$ in group V. Reason (R): $NH X_{4} X^{+}$ lowers $[CO X_{3} X^{2 -}]$ through $NH X_{4} X^{+} + CO X_{3} X^{2 -} NH X_{3} + HCO X_{3} X^{-}$ , and $MgCO X_{3}$ is considerably more soluble than the group V carbonates, so its ionic product stays below $K_{s p}$ .

The ammonium ion converts carbonate to hydrogencarbonate, lowering

[CO X_{3} X^{2 -}]

. The relatively soluble

MgCO X_{3}

then does not reach its

K_{s p}

, whereas

BaCO X_{3}

SrCO X_{3}

and

CaCO X_{3}

do. Both statements are true and R explains A.