Consider the three mercury manometers shown here. One of them has 1 mL of water on top of the mercury, another has $1 \mathrm{mL}$ of a $1 \mathrm{m}$ urea solution on top of the mercury, and the third one has $1 \mathrm{mL}$ of a 1 $m$ NaCl solution placed on top of the mercury. Which of these solutions is in the tube labeled X, which is in $Y,$ and which is in $Z ?$