Correct answer: (1)

Fluorine and Iodine both belong to a group of elements known as halogens. They share similar properties as a result of the number of available electrons in their valence orbital. However, fluorine is first of the halogens in the periodic table and has an atomic number of nine (9), while iodine is one of the last halogens and has an atomic number of fifty three (53). Iodine as a result has a much greater number of electrons at 53 than fluorine at 9. Intermolecular or Van Der Waals forces are responsible for the formation of liquids and solids when they are greater than the kinetic energy of the molecule. The intermolecular forces are also generally stronger for molecules that contain a greater number of electrons as is the case for iodine.

Answering the question:

When answering this question there are two things that should be understood beforehand.

Firstly an idea of where on the periodic table iodine is relative to fluorine. The fact that the question states that fluorine is a gas and iodine is a solid is an indicator that iodine is probably lower down the group in periodic table than fluorine.

Secondly it would be important to understand the interaction between kinetic energy and intermolecular forces. Kinetic energy is the energy that would keep the molecules in motion, however intermolecular forces are the forces of attraction that one molecule would have with another when they are close enough to each other. When the intermolecular forces of attraction are able to overcome the kinetic energy then a liquid or solid is the result.

Therefore when comparing why a molecule exists as a gas or a solid the intermolecular forces play a greater role than the kinetic energy leaving only (1) and (2) as the possible answers. The intermolecular forces of fluorine have to be weaker than those of iodine in order for fluorine to be a gas and iodine a solid.

This leaves (1) as the correct answer