Final answer:
The halogens should be ordered in terms of decreasing boiling points as I2 > Br2 > Cl2 > F2, corresponding to Option A, due to the difference in dispersion forces which increase with larger and heavier atoms.
Step-by-step explanation:
To arrange the halogens Br2, I2, F2, and Cl2 in order of decreasing boiling points, one must consider the size and molecular weight of the molecules. As a general trend, larger and heavier atoms and molecules exhibit stronger dispersion forces than do smaller and lighter ones.
The boiling point of a substance is significantly influenced by these forces. F2 and Cl2 are gases at room temperature, suggesting they have weaker attractive forces and lower boiling points compared to Br2 which is a liquid, and I2 which is a solid under the same conditions.
This implies that iodine (I2) has the strongest dispersion forces and therefore the highest boiling point, followed by bromine (Br2), then chlorine (Cl2), and finally fluorine (F2) which has the weakest forces and lowest boiling point. The correct order of decreasing boiling points for the given halogens is therefore I2 > Br2 > Cl2 > F2, which corresponds to Option A.