Question

Xenon does not form fluorides such as XeF3 and XeF5

Answer 1

Because it does not have unpaired electron

Answer 2

All the filled orbitals of Xe have paired electrons. The promotion of 1, 2 or 3 electrons from the 5p filled orbitals to the 5 d vacant orbitals will give rise to 2, 4 and 6 half-filled orbitals. Therefore, Xe can combine with even number of F-atoms but not odd.