For the metal - olefin complexes (i) $\left[\mathrm{PtCl}_{3}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)\right]^{-}$and (ii) $\left[\mathrm{PtCl}_{3}\left(\mathrm{C}_{2} \mathrm{F}_{4}\right)\right]^{-}$, the correct statement is that
(a)carbon - carbon bond length is same both in (i) and (ii)
(b)carbon - carbon bond legnth in (i) is smaller compared to that of (ii)
(c)carbon - carbon bond length in (i) is larger compared to that of (ii)