Increasing amount of solid HgI2 is added to 1 L of an aqueous solution containing 0.1 mol KI. Which of the following graphs do represent the variation of freezing point of the resulting solution with the amount of HgI2 added?

When HgI2 is added to KI:HgI2       +        2KI    →    K2HgI4 -                      0.05               0.1 -                       -                   0.05⇒0.05 moles of HgI2 are required for its complex reaction with KI.Thus, as HgI2 is being added, the number of solute molecules will decrease causing ∆Tf to decrease ⇒ (Causing Tf to increase). When whole of KI has been converted to K2HgI4 further addition of HgI2 does not change Tf since it is a sparingly soluble salt.