(a) It fails to explain the incomplete octet of the central atom.
Examples: The central atom Li, Be and B in LiCl, BeCl2 and BCl3 have 1,2 and 3 valence electrons only respectively.
(b) The octet rule is not satisfied for the atoms in a molecule having an odd no of electrons.
Examples: NO and NO2
(c) The octet rule cannot be applied in case of elements in and beyond the third period of the periodic table since these elements have more than 8 electrons.
Examples: PF5, SF6,H2SO4 etc.,
(d) This rule fails to explain the shape and relative stability of molecules.