Question

allen decided magnesium was the most effective at preventing rust, but his results are actually inconclusive. what mistake did he make?

Explanation:

To determine the mistake, we need to recall the principles of experimental design. In a valid experiment, there should be only one independent variable (the factor being tested - in this case, the type of nail coating like magnesium, aluminum, etc.). However, looking at the table, the type of nail (e.g., common iron nail, roofing iron nail, etc.) also varies. This means there are two variables (nail type and coating) changing simultaneously. According to the scientific method, when multiple variables change, it's impossible to isolate the effect of the variable of interest (the coating - which Allen thought was magnesium). So the mistake is having more than one independent variable.

Answer:

Allen had more than one independent variable (both the type of nail and the coating material were changing).