Final answer:
To determine the order of decreasing dipole moments, you consider the bond length and electronegativity differences. The C-F bond typically has the highest dipole moment. Without the specific molecules provided in the question, it's impossible to rank them correctly from the options given.
Step-by-step explanation:
To place substances in order of decreasing dipole moment, you must consider both the bond length and the electronegativity difference between the bonded atoms. As electronegativity decreases in the order F > Cl > Br > I and bond length increases in the opposite order, one can infer that the strongest dipole moment will be associated with the C-F bond due to its shortest bond length and highest electronegativity difference.
When comparing substances with C-halogen bonds, C-F will have the greatest dipole moment due to the combination of a shorter bond length and higher bond dissociation energy, which also correlates with a stronger bond. As you move to C-Cl, C-Br, and C-I, the dipole moments decrease since the electronegativity difference decreases and the bond length increases. However, the exact order of the substances was not provided in the question, thus making it impossible to organize them correctly into one of the options given (1 to 5) without additional context.