Question

my question is Why?

Answer 1

why is it induced dipole and not covalent?

Answer 2

@Kainui

Answer 3

Well a covalent bond would be the bonds within the molecule itself being broken. Simply heating it is just breaking those molecules away from the rest of the molecules in the crystal. so if that makes sense, this picture is a "crystal" with I2 molecules in it. When it's heated enough the molecules break free of each other but are still I2 molecules, since you have only gently heated it you're not going to get radicals of single Iodine atoms floating around.