# Multiple choice: Soap in Hard Water. What is the correct solution and why?

Surely it is sample $A$?
You assess water hardness, and the Table gives you the means to do this. Sample $A$ requires the most soap to give a decent lather. It also has the greatest boiling point, and the most precipitate when treated with $A {g}^{+}$ (i.e. the greatest concentration of $H {O}^{-}$).
I am willing to bet that if they had tabulated $p H$ of each sample, sample $A$ would have had the highest $p H$.