Concept:Chlorine gas from the reaction is moist, so it must be dried using a drying agent that does not react with chlorine.Explanation:Potassium tetraoxomanganate(VII) oxidises concentrated hydrochloric acid to produce chlorine gas.The gas carries water vapour and must be dried.Concentrated tetraoxosulphate(VI) acid absorbs water and does not react with chlorine.Alkaline substances like calcium oxide and sodium hydroxide would react with chlorine, so they cannot be used.Answer:A. Concentrated tetraoxosulphate (VI) acid