A student investigated the effect of salt concentration on pieces of potato. The method involved repeating the experiment with different concentrations of salt solution.

What is the independent variable in the investigation?

In a scientific investigation, the independent variable is the factor that is intentionally changed or manipulated by the researcher to observe its effect on the dependent variable. In this experiment, the student is investigating the "effect of salt concentration". The method explicitly states, "Repeat steps 1 to 6 using different concentrations of salt solution." This shows that the concentration of the salt solution is the variable being changed. The change in mass of the potato is the dependent variable (what is measured), while factors like time, volume of solution, and initial size of potato pieces are control variables.