Expalin the following
(a) The central `C-C` bond in Buta 1,3 diene is shorter than that of n-butane
(b) Why the dipole moment of `cis-1,2` dichloroethene is greater than that of trans -1,2 -dichloroethene
(c ) `CIF_(2)^(Θ)` is linear, but `CIF_(2)^(o+)` is bent
(d )Two different bond lengths are observed in `PF_(5)` but only one bond lenght is observed in `SF_(6)` .

Explanation

Due to resonance in conjugated dienes In the the cis compound the dipoles do not cancel each other and the resultant is a higher value while in the trans compound `C-CI` bond dipoles are equal and opposite and hence cancel each other and `mu =0`
(c ) In `CIF_(2)^(Θ)` ion the central chlorine atom involves `sp^(3)` d hybridisation to have minimum electronic repulsion Three lone pairs should be in equatorial position to give linear shape to the ion Whereas in case of `CIF_(2)^(o+)` ion the central chlorine atom involves `sp^(3)` hybridisation having two lone pairs resulting in bent shape for the ion (bond angle less than `109^(@)28'` due to bp-lp repulsion)
(d) `PF_(5)` has trigonal pyramidal structure `sp^(3)` d hybridisation of central atom) in which bond angles are `90^(@)` and `120^(@)` respectively and there are two types of bonds axial and equatorial (axial being longer than equatorial) In case of `SF_(6)` the structure is octahedral (`sp^(3)` hybridisation of the central atom `S`) resulting only one type of bond bond angle `90^(@)` and one type of bond lenght
.