Question

Why is iodine a good nucleophile as well as a good leaving group?

Answer 1

Because, Iodine has three lone pair of electrons, it it thus a very good nucleophile.
However, it's a very good leaving group too, because of its large size and the reason is that the bond of iodine with carbon is very very weak.
Hence, iodine atom is a good nucleophile as well as a good leaving group.

Answer 2

Iodine is a good leaving group and a good nucleophile.

• Iodine is a halogen.
• It resides in group 17.
• Iodine has three electrons. So, iodine can easily donate its electron to any compound and act as a good nucleophile.
• Again Iodine is larger among halogens so, the bond with iodine is very weak. Thus due to weak bonds iodine can be easily removed and act as a good leaving group.