He thought elements that haven't been discovered belonged in the place of the gap. He could also use the atomic mass of the missing elements
A controlled variable is the one that is kept constant, the manipulated variable is the independent variable in an experiment , it is called manipulated because is the one that can be changed. A responding variable or variables are the dependent variables that change as a result of the changes in the manipulated variable.
Answer A )
Potassium chloride
K+ Cl-
hope this helps!.
