Answer
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Work Step by Step
Aromatic electrophilic substitution reaction occurs when an electrophile ($E^{+}$) attacks the benzene nucleus due to presence of electron densed ring in benzene and produce monosubstituted benzene by substitute one H atom of benzene ring.
In presence of iron (III) catalyst, chlorine gas generates $Cl^{+}$ electrophile which can participate in aromatic electrophilic substitution reaction with the benzene ring of $C_{6}H_{5}CH_{3}$ & produce o-chlorotoluene and p-chlorotoluene. This happens because due to resonance effect (+R effect) of $'CH_{3}'$ group, the ortho and para position are more electron dense & it is easy for an electrophile to attack on these sites to produce ortho and para products.
On the other hand, when the reaction is light-catalyzed with no $Fe^{3+}$ catalyst present, aliphatic substitution reaction takes place where one aliphatic H attached with aliphatic 'C' atom is substituted by one Cl atom through free radical mechanism & produce $C_{6}H_{5}CH_{2}Cl$.
