Which is the most easily liquefiable rare gas?

Which of the following pairs is incorrectly matched?

Gradual addition of electronic shells in the noble gases causes a decrease in their

The number of peroxide bonds in the perxenate ion $[XeO_6]^{4-}$ is ........

Fluorine forms chemical compounds with

The correct decreasing order of the following $Xe$ compounds to act as both fluorinating and oxidizing agent is
$(I)$ $XeF_6$
$(II)$ $XeF_4$
$(III)$ $XeF_2$