Answer: B. temperature, acidity, mineral composition and surface area
Independent variables are those which can be changed and manipulated in the experiment the effect of which can be observed on the changes that occur in the dependent variable. For example the effect of quantity of manure and water on the height of the plant. Here, quantity of manure and water are the independent variables and the height is the dependent variable.
The temperature is the independent variable because the level of temperature can be increased or lowered down manually.
The acidity is the independent variable because the acidity can be manipulated by addition of chemicals that exhibit more hydrogen ions.
Mineral composition can be manipulated and it is an independent variable by treating a mineral with a suitable chemical this will bring a change in the chemical composition of the mineral.
Surface area is the independent variable because it is the total area required for the conduction of the experiment . The surface area can be increased or decreased.
