Benzyl chloride undergoes S\(_{N}\)1 reactions easily because the benzylic carbocation formed is stable due to resonance stabilization. Chloro benzene, on the other hand, does not undergo S\(_{N}\)1 reaction readily because the lone pair of electrons on the oxygen atom of the aromatic ring is delocalized, making the C-Cl bond more stable and less likely to dissociate.
Hence, the assertion (A) and reason (R) are correct and R correctly explains A.