Which best describes the purpose of a control sample?

A control sample serves as a sample used to eliminate errors or minimize them. Also, it is used to prevent the effect of one parameter which is not the subject being studied. For instance, in an adsorption experiment a control sample is always included wherein in a flask  it only contains the adsorbate solution. The said sample is responsible for calculating how much of the adsorbate is being adsorbed on the sides of the flask.

Answer:

a. energy is absorbed in the reaction.

explanation:

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.

Use a magnet to separate iron, evaporate water, i'm not sure how to separate the other two i'm sorry but good luck