To determine which compound has the shortest C-Cl bond, we need to analyze the nature of the bonds in each compound.
The C-Cl bond attached to a carbon in a benzene ring has resonance and has double bond character.
The C-Cl bond length is relatively long due to the single bond.
The nature of the C-X bond is different for Haloalkanes and Haloarenes.
Haloalkanes: Halogen atoms are more electronegative than carbon. Due to this, they share pair of electrons that lies closer to the halogen atom.
As a result, the halogen carries a small negative charge i.e. δ- while the carbon carries a small positive charge i.e. δ+. As we go down the periodic table, the size of the halogen atom increases. The fluorine atom is the smallest and the iodine atom is the largest. so the carbon-halogen bond length also increases C-F to C-I. Further, as we move from F to me, the electronegativity of the halogen decreases, therefore, the polarity of the C-X bond and hence dipole moment of the haloalkane should also decrease.
Haloarenes: In the case of haloarenes carbon of the benzene ring attached to a halogen is sp2 hybridised which have a short length and can hold more electron pair and the C-X bond is polar in nature. so the lone pair of electrons undergo the resonance with the benzene ring due to this delocalisation of the lone pair of electrons leading to the formation of double character.
The C-X bond of haloalkanes is more polar than the C-X bond of haloarenes. This is due to the higher electronegativity of halogen over carbon.
There is a delocalized lone pair of electrons on the X atom present over the benzene ring which results in the double bond character in the C-X bond of haloarenes.
As we move in the periodic table the atomic size down the group increases hence C-X bond length in haloarenes also increases.
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