To determine which of the listed solutions has the lowest freezing point, we need to consider the number of particles formed in each solution when it dissolves.
The freezing point depression depends on the concentration of solute particles in a solution. The more solute particles there are, the greater the freezing point depression.
Let's analyze each of the listed substances:
NaNO2: When NaNO2 dissolves, it dissociates into Na⁺ ions and NO₂⁻ ions. So, one mole of NaNO2 produces two particles (Na⁺ and NO₂⁻).
NaCl: NaCl also dissociates in water, forming Na⁺ ions and Cl⁻ ions. One mole of NaCl produces two particles (Na⁺ and Cl⁻).
Ca(NO3)2: Calcium nitrate, Ca(NO3)2, dissociates into Ca²⁺ ions and two NO₃⁻ ions. So, one mole of Ca(NO3)2 produces three particles (Ca²⁺ and two NO₃⁻).
CuSO4: Copper(II) sulfate, CuSO4, dissociates into Cu²⁺ ions and SO₄²⁻ ions. One mole of CuSO4 produces two particles (Cu²⁺ and SO₄²⁻).
Comparing the solutions, we can see that Ca(NO3)2 forms the highest number of particles (three) for every mole of solute. Therefore, it will have the greatest freezing point depression among the listed substances. Consequently, Ca(NO3)2 solution will have the lowest freezing point.
In summary, among the listed substances of the same molality, the Ca(NO3)2 solution is expected to have the lowest freezing point.