Concept:Acidified K2Cr2O7 turns from orange to green when it is reduced by a compound that can be oxidized, such as an alcohol vapour in the breath.Explanation:In the test, Cr2O72− ions are orange in colour.When a person breathes into the tube, ethanol vapour from the breath reduces the orange dichromate ion to green Cr3+ ions.This colour change is used in the breathalyzer test to detect alcohol.Alcohols belong to the alkanol family, so the result indicates the presence of an alkanol.Answer:C. alkanol