Explain the following :
(a) The electron gain enthalpy with negative sign for fluorine is less than for chlorine, still fluorine is a stronger oxidising agent than chlorine.
(b) `XeF_(2)` is linear molecule without a bend.
(c) `NCl_(3)` is an endothermic compound while `NF_(3)` is an exothermic one.

Answer

(i)The instability of `NCl_(3)` is due to the weak NCl bond.This is due to the large difference in the size of nitrogen and chlorine atoms.On the other hand, atoms of both nitrogen (75 pm) and fluorine (72 pm) are small sized.Thus, bonding in `NF_(3)` is quite strong and it is an exothermic compound.
(ii)`XeF_(2)` has two bonded pairs and three lone pairs of electrons which are placed at equitorial position so as to minimize repulsion.Therefore `XeF_(2)` is linear without a bend.
(iii)It is because `F_(2)` has higher standard reduction potential due to lower bond dissociation energy and higher hydratin energy of `F^(-)` ion.