Which of the following properties of the elements chlorine, bromine and iodine increases with increasing atomic number?

The ionization energies of halogens decrease on moving down the group.

Similarly the bond dissociation energies decrease from chlorine to bromine to iodine.

With increase in the atomic number, the atomic and ionic radii of hydrogen increases from fluorine to iodine.

Also, the melting points and the boiling points increase in the same order.

Hence, the enthalpy of vaporization also increases in the same order.