Question

reason for the boiling point DECREASING order
R-I > R-Br > R-CI
why does Iodine alkyl group has highest bp

Answer 1

The boiling points of alkyl halides decrease in the order RI> RBr> RCl> RF. This is because as the size of halogen increases, the magnitude of van der Waals forces increase, and hence the boiling point increase

The main factor affecting the boiling point is the molecular weight.

The other factor affecting boiling point is the nature and strength of intermolecular interactions, usually in the order ionic > hydrogen bond > dipole-dipole > Van der Waals.

In the comparison of RF vs RI boiling point, molecular weight is definitely in favor of higher boiling points for RI, at least for small molecules. It is true that the C-F bond is much more ionized than C-I so it will create stronger dipole-dipole interactions but not sufficiently to compensate for the effect of the mass increase.
This is why alkyle iodide has higher boiling point.