XeF4 and SO2 both are symmetrical
Symmetrical species are those which can be divided into equal halves by a line of symmetry passing though them. This is possible only in those figured which have a well defined point of symmetry.
Option a has a structure in which xenon atom is surrounded by 4 fluorine atoms. It is thus divided into two equal halves by a line of symmetry passing through the centre.
Option c has sulphur atom surrounded by oxygen atoms which makes it symmetrical due to a line of symmetry passing through the middle. This, it is symmetrical.