Write the various isomers of C7H8Cl containing benzene ring. Which of these has waekest C-Cl bond ?

Compound with Molecular formula C7H​8Cl containing benzene does not exist. Molecular formula should be C7H7Cl. Since compound has benzene ring (C6H6), then we are left with CHCl. 
So benzene can be mono-substituted or di-substituted. Therefore isomers of C7H7Cl are -

In last isomer, Cl is attached to sp3 carbon, there is no double bond character in the bond. So it is purely single bond. Hence it has the weakest bond among all the compounds.
While in the compounds, with Cl in the benzene ring, due to resonance there is double bond character in C-Cl bond. So it is stronger. 

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