(a) Draw the molecular structure of following compounds :
(i) `XeF_(6)`
(ii) `H_(2)S_(2)O_(8)`
(b) Explain the following observations :
(i) The molecules `NH_(3)` and `NF_(3)` have dipole moments which are of opposite direction.
(ii) All the bonds in `PCl_(5)` molecule are not equivalent.
(iii) Sulphur in vapour state exhibits paramagnetism.

Explanation

(a) (i) `XeF_(6)` can also be prepared by the interaction of `XeF_(4)` and `O_(2)F_(2)` at `143 K`.

b(i)

Since'N' is more electronegative than `H`, hence the dipole is pointing towards `'N'` in `NH_(3)`. In `NF_(3)`. F is more electronegative than 'N' hence the dipole is pointing towards `'F'`.
(ii) The three potential P-Cl bonds are equivalent , while the other two axial bond are longer than equatorial bonds. This is due to the fact that the axial bond pair suffer more repulsion as compared to equatorial bond pair.

(iii) In vapour state sulphur partly exists as `S_(2)` molecule which has two unpaired electrons in the antibonding `pi` orbital like `O_(2)` and hence exhibit paramagnetic behaviour.