Explain the following facts giving appropriate reason in each case :
(i) `NF_(3)` is an exothermic compound whereas `NCl_(3)` is not .
(ii) All the bonds in `SF_(4)` are not equivalent

Explanation

The larger different in size of N and Cl results in the weakness of strength of N-Cl bond .
On the other hand , the difference in size of N and F is small , consequently , the N-F bond is quite strong . As result , `NF_(3)` is an exothermic compound .
(ii) In `SF_(4)` there as three equal equatorial bond and two axial bonds , the axial bonds are longer due to more inter atomic repulsions between the F atoms . Therefore , all the bonds in `SF_(4)` are not equal . The hybridisation of `SF_(4)` in `SP^(3)d.`