In ${\mathrm{XeF}}_2,{\mathrm{XeF}}_4\text{ and }{\mathrm{XeF}}_6$ the number of lone pairs on Xe are respectively 

In ${\mathrm{XeF}}_2$Total number of valence electrons of $\mathrm{Xe}=8$two electrons shared with 2F atoms, 6 electrons left hence 3 lone pairs, 

in XeF ₄,4 shared with 4 F atoms 4 left hence 2 lone pairs; 

in XeF₆, 6 shared with 6 F atoms 2 left hence 1 lone pair.