The formula that correctly represents the product of an addition reaction between ethene and chlorine is C2H4Cl2
Addition reaction occurs when an atom is added to a compound that has a double bond or triple bond (unsaturated hydrocarbons). Unsaturated compounds are associated with addition reactions. For example Ethene is an example of unsaturated hydrocarbon; when reacted with chlorine gas , chlorine atoms are added to each carbon atoms.