Chemistry · EQUILIBRIUM

When \( \text{HCl} \) gas is passed through a saturated solution of \( \text{NaCl} \), pure \( \text{NaCl} \) precipitates out while impurities like \( \text{MgSO}_4 \) and \( \text{Na}_2\text{SO}_4 \) remain dissolved. The underlying reason for this phenomenon is:

1. A
   Decrease in temperature of the solution upon dissolution of \( \text{HCl} \)
2. B
   Chemical reaction between \( \text{NaCl} \) and gaseous \( \text{HCl} \) forming an insoluble adduct
3. C
   Formation of a complex ion between \( \text{Mg}^{2+} \) and \( \text{Cl}^- \)
4. D
   Common ion effect increasing \( [\text{Cl}^-] \), causing the ionic product of \( \text{NaCl} \) to exceed its \( K_{sp} \)