The element of the VIA group which cannot form Hexa halides is;

 Oxidation states of VIA group elements in these halides are $+1,+2,+4$ and $+6$ respectively. Group VIA elements form ${\mathrm{MX}}_6$ type of Hexa halides. Among hexahalides, only hexafluorides are stable. They have octahedral structures. Oxygen cannot form Hexa halides as its valence electrons are located in the $2\mathrm{p}$-subshell, one full energy level, and also due to the absence of vacant $\mathrm{d}$-orbital, it can't excite.