1. **Stating the problem:** We are given a solution with calcium ion concentration Ca$^{2+}$ of 3.2 g/L and 3.2 \times 10^{-3} M (molarity). We want to understand the relationship between these values. 2. **Formula and concepts:** Molarity (M) is defined as moles of solute per liter of solution. The mass concentration (g/L) is the mass of solute per liter of solution. 3. **Calculate molar mass of Ca$^{2+}$:** Calcium atomic mass is approximately 40.08 g/mol. 4. **Convert molarity to mass concentration:** $$\text{mass concentration} = \text{molarity} \times \text{molar mass}$$ 5. **Substitute values:** $$3.2 \times 10^{-3} \text{ mol/L} \times 40.08 \text{ g/mol} = 0.128256 \text{ g/L}$$ 6. **Compare with given mass concentration:** Given is 3.2 g/L, calculated is 0.128256 g/L, which is much smaller. 7. **Interpretation:** The given 3.2 g/L does not correspond to 3.2 \times 10^{-3} M for Ca$^{2+}$. Possibly, the 3.2 g/L refers to total calcium compound, or there is a mistake. **Final answer:** The molarity 3.2 \times 10^{-3} M corresponds to approximately 0.128 g/L of Ca$^{2+}$, not 3.2 g/L.