When mercuric iodide is added to the aqueous solution of potassium iodide the

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When mercuric iodide is added to the aqueous solution of potassium iodide the freezing point is raised as Δ T f decreases due to complex formation number of species decrease and molecular weight increases. ΔT f ∝ 1 Molecular weight ∝ number of species H g I 2 although insoluble in water but shows complex formation with KI as 2KI + HgI 2 → K 2 HgI 4 2KI → 2K + +2I − (4 ions) K 2 HgI 4 → 2K + HgI 4 − 2 (3 ions) Here number of species decreases due to the reaction. Hence, ΔT f ↓ and T f ↑