Answer: A2X, δHvap= 39.6 kj/mol is the correct answer.
Explanation: Heat of Vaporization is defined as the minimum amount of energy required to convert a liquid substance into a gas. In liquids the intermolecular forces are stronger as compared to gases. In order to break these intermolecular forces a heat is supplied. Now, depending upon the nature of these interactions the amount of heat required varies. Stronger the intermolecular forces greater will be the energy required to break them. Hence in above statement the greatest energy is associated with compound A2X (39.6 kJ/mol) as compared to others, therefore it will be having strongest intermolecular forces as compared to other given compounds.