A variable whose variation does not depend upon on any other variable in any manner is termed as independent variable.
An independent variable is the one that can only be actually varied by the experimenter who is using it to test the affect of this particular variable on other variables that depend on it and thus, change as the independent variable is changing.
In the given experiment the scientist is testing the effect of spraying chemicals on the apple yard, here<em> the chemical used is an independent variable as varying the amount of chemical that is sprayed will change the yield of the apples. </em>
