A yellow metallic powder is burnt in a stream of fluorine to obtain a colourless gas X which is thermally stable and chemically inert. Its molecule has octahedral geometry. Another colourless gas Y with same constituent atoms as that of X is obtained when sulphur dichloride is heated with sodium fluoride. Its molecule has trigonal pyramidal structure. X and Y are respectively
A. `SF_(4) and S_(2)F_(2)`
B. `SF_(6) and SF_(4)`
C. `NaF and NaC1`
D. `SF_(4) and SF_(6)`
