The answers would be:
1. Dependent Variable: Extent of Corrosion of Metals
A dependent variable is a variable in an experiment which is under study or observation and varies with respect to the independent variable. In this experiment, Madison wants to check the effect on the progression of corrosion of metals with regard to changes in salt concentration, which means corrosion is under observation for any variation with fluctuations in salt concentration of air.
2. Independent Variable: Salt Concentration in Air
An independent variable is a variable that is controlled (increased or decreased, for example), and is known. This variable is not influenced by another variable, for example: a change in salt concentration in air may have an effect on the corrosion of metals, but the phenomena that is the corrosion of metals does not influence the salt concentration in the air.
3. Confounding Variable: Speed of Air
A confounding variable is one which has the capacity to influence/change both the dependent and the independent variable. If the speed of air is higher, it will carry particles of salt at a faster speed and rate (higher kinetic energy) which will result in an increased corrosion of metals. Similarly if the air speed is slower, the corrosion of metals will be decreased. Speed of air also influences the salt concentration as different air currents have the capacity to carry different levels of salt content from the air above the ocean with them.
Hope this helps!