Melting point of hydrogen halides (HF, HCl, HBr, and HF) follows the order of
HI> HBr> HCl> HF
HI> HF> HBr> HCl
HF> HCl> HBr> HI
HBr> HI> HCl> HF
The correct order of melting point of HF, HCl, HBr, and HI is: HI> HF> HBr> HCl as 222K, 190K, 185K and 159K respectively.This is due to highest electronegativity of fluorine and strong hydrogen bonding between fluorine and hydrogen whereas HI has higher molecular mass than HF, due to this Vander waals forces of attraction gets defeat the intermolecular hydrogen bonding.