Which of the following is a dependent, controlled or independent variable? metal, vinegar, plastic bowls and spoons, time, and hydrogen peroxide.
The question does not specify what the various ingredients are used for and it would be difficult to answer without that information. I am assuming you are trying to generate the patina on steel or iron by using vinegar and hydrogen peroxide. This method can be used to produce a tarnished look or antique look on objects. In this process, we first etch the surface with vinegar and then apply hydrogen peroxide (And some sale) to obtain the desired tarnished look.
Let us understand what different types of variables are. The variables that are varied are the independent variables and we study their effect on dependent variables. Controlled variables do not change during the experiment. In this case, we can vary the amounts of hydrogen peroxide, vinegar and time and study their effects on metal surface or metal itself. The plastic bowls and spoons are only used for adding the liquids and placing metal in. Based on our definition, here is the classification of variables:
Controlled variables: plastic bowls and spoons
Dependent variables: metal (or metal surface, to be more precise)
Independent variables: vinegar, hydrogen peroxide and time
Hope this helps.