"Hybridisation of central atom does not always change due to back bonding". This statement is valid for which of the following compounds?

($\mathrm{i}$) ${\mathrm{CCl}}_3^{-}$
($\mathrm{ii}$) ${\mathrm{CCl}}_2$
($\mathrm{iii}$) ${\mathrm{CF}}_2$
($\mathrm{iv}$) $\mathrm{N}{\left({\mathrm{SiH}}_3\right)}_3$

According to following reactions, 

${\mathrm{CHF}}_3\stackrel{\mathrm{K}\alpha }{⟶}{\mathrm{CF}}_3^{-}+{\mathrm{H}}^{+}$

${\mathrm{CHCl}}_3\stackrel{{\mathrm{K}}^{\text{'}}\alpha }{⟶}{\mathrm{CCl}}_3^{-}+{\mathrm{H}}^{+}$

Which one is the correct statement from the following options ?

Which of the following pair of compounds are homologous :-