Answer
a) Amount of salt added (Independent Variable)
b) Freezing point (Dependent Variable)
Work Step by Step
a) Independent Variable is a variable that is being changed or manipulated and in the experiment the Amount of salt added is being changed. Thus, the Amount of salt added is the Independent Variable.
b) Dependent Variable is a variable that is not changed and depends on the independent variable and in the experiment the freezing point is not being changed. Thus, the freezing point is the dependent Variable.