Which aqueous solution of ki freezes at the lowest temperature?
(1) 1 mol of ki in 500. g of water
(2) 2 mol of ki in 500. g of water
(3) 1 mol of ki in 1000. g of water
(4) 2 mol of ki in 1000. g of water

The answer is (2) 2 mol of KI in 500. g of water.. This is a question of colligative properties. Boiling point elevation and freezing point depression depend on the concentration of dissolved solute. You would get the greatest concentration of KI with the largest moles of KI and smallest volume of water.

The mass has escaped into a gas which you can not see so the law stays true.