The iodide is a better leaving group.
Work Step by Step
1. Identify the possibles leaving groups: - $Iodide $($I^-$) - $Water$ ($H_2O$) 2. Determine which one is better. - In this section, we've learned that some halides, like iodide, are good leaving groups (page 219). - And we have also learned that $H_2O$ is a good leaving group too (page 218). But, if we look at the image in page 218, we will see that, the $I^-$ is more stable than $H_2O$. Therefore, iodide is a better leaving group. ** You can also compare the strength of the conjugate acids, so: - $H_3O^+$ and $HI$. $HI$ is stronger, therefore, $I^-$ is a better leaving group