Answer:
Independent: sizes of nails
Dependent: number of paper clips
Controlled: Battery, wire and type of nails
Explanation:
An independent variable is a variable which when changes does not the effect the results of the experiment. It does not depends upon the dependent variable.
A dependent variable is defined as a variable which is affected when the independent variable is changed by the researcher or the experimenter. It depends greatly upon the independent variable.
While a controlled variable is that variable whose value is not changed in an experiment. It contains all the constants.
In the context,
the independent variable are : sizes of nails
the dependent variables are : number of paper clips
the Controlled variables are: Battery, wire and type of nails