Answer:
the mass of salt
Step-by-step explanation:
In an experiment, we have an independent variable and dependent variable. The independent variable is the variable that is manipulated to cause changes in other variable while the dependent variable is the variable that responds to the changes made to the independent variable and is measured.
In this case of experiment, the mass of the salt is the DEPENDENT VARIABLE while the different temperatures is the INDEPENDENT VARIABLE. In a graphical representation, the independent variable is always plotted on the x-axis or horizontal axis while the dependent variable is always plotted on the y-axis or vertical axis.
Since the dependent variable is the mass of the salt, it should be plotted on the y axis.