Antioxidants are important and necessary food additives. These help in food preservation by retarding the action of oxygen on food. They act through several chemical mechanisms. Butylated hydroxy anisole (BHA) is one of the familiar antioxidant. The addition of BHA to butter increases its shelf life from months to years as it is more reactive towards oxygen than food. Hence, both Assertion and Reason are correct and Reason is the correct explanation of Assertion.