Amedical researcher has isolated a chemical from cigarette smoke. when the scientist mixes a small amount of the substance with living human cells, the chemical damages unsaturated fatty acids in the cells' plasma membranes. he is able to prevent this damage by adding vitamin e to the mixture of the chemical and cells. based on this information, the scientist has

Determined that the chemical in cigarette smoke is an oxidant.

Explanation:

Basically, an oxidant is a reactant that oxidizes or removes electrons from other reactants during a redox reaction. What the medical researcher is trying to do is looking at each element's oxidation state before and after the reactant and then preventing the damage by adding vitamin E to the mixture, therefore determining that cigarette smoke is an oxidant.