The correct answer is option 2, yeast. Alcohol fermentation is a process in which sugars are converted into alcohol and carbon dioxide by the action of enzymes produced by microorganisms. In this case, yeast is responsible for alcohol fermentation. Yeast is a type of fungus that belongs to the Saccharomyces genus. It is commonly used in baking and brewing processes. Yeast consumes sugars and produces ethanol (alcohol) and carbon dioxide as byproducts. This process is utilized in the production of alcoholic beverages such as beer, wine, and spirits. Chlorella (option 1) is a type of algae, Agaricus (option 3) is a genus of mushrooms, and Puccinia (option 4) is a genus of plant pathogens, none of which are involved in alcohol fermentation.