Which of the following correctly ranks the leaving groups from worst to best?

• A. ${\mathrm{Br}}_{-}$ < ${\mathrm{Cl}}_{-}$ < $F_{-}$ < $I_{-}$
• B. $I_{-}$ < ${\mathrm{Br}}_{-}$ < ${\mathrm{Cl}}_{-}$ < $F_{-}$
• C. $F_{-}$ < ${\mathrm{Cl}}_{-}$ < ${\mathrm{Br}}_{-}$ < $I_{-}$
• D. ${\mathrm{Cl}}_{-}$ < $F_{-}$ < ${\mathrm{Br}}_{-}$ < $I_{-}$

Answer: (C)

Verified step by step guidance

1. Understand that the ability of a leaving group to depart depends largely on its stability once it has left, which is often related to the conjugate base's stability.
2. Recall that among halide ions (F⁻, Cl⁻, Br⁻, I⁻), the larger the ion, the more stable it is due to better charge distribution and lower charge density.
3. Recognize that the order of leaving group ability generally follows the trend: I⁻ > Br⁻ > Cl⁻ > F⁻, because iodide is the largest and most stable, while fluoride is the smallest and least stable.
4. Use this trend to rank the leaving groups from worst to best as: F⁻ < Cl⁻ < Br⁻ < I⁻.
5. Confirm that this ranking matches the correct answer given, and understand that any other order contradicts the fundamental principles of leaving group stability.