At room temperature, iodine is solid, bromine is liquid and chlorine exist in gaseous phase due to following factor(s):

 

At room temperature, iodine is solid, bromine is liquid and chlorine exists in the gaseous phase due to surface area,) molecular volume, and ease of polarization.

Each substance's molecules are drawn to one another by dispersion (London) intermolecular forces. The equilibrium between the kinetic energy of the molecules and their intermolecular attractions determines whether a material is a solid, liquid, or gas.

The electrons are farther away from the nuclei in iodine, allowing for easier distortion of the electron clouds. The forces of London's dispersion get ever greater.

The molecules will all become solids at a low enough temperature. They will all become gases if the temperature is high enough.

Fluorine and chlorine are only solids between $-7^{\circ }\mathrm{C}$and ${59}^{\circ }$, but bromine and iodine are solids at all different temperatures.

Hence, option D is correct.