Chlorination of toluene involves the substitution of hydrogen atoms with chlorine atoms in the toluene molecule. This reaction can occur under different conditions and can lead to the formation of different products. The true statements about chlorination of toluene are:

a) In the presence of light, benzyl chloride is formed:
- When toluene is exposed to light, it undergoes a free radical substitution reaction. The chlorine molecule (Cl2) is broken down by the light to form highly reactive chlorine atoms (Cl•).
- The chlorine atoms then react with the toluene molecule, abstracting a hydrogen atom from the benzene ring and forming a benzyl radical (C6H5CH2•).
- The benzyl radical can then react with a chlorine atom to form benzyl chloride (C6H5CH2Cl). This reaction can occur at any position on the benzene ring, resulting in the formation of different isomers.

b) In the presence of AlCl3, ortho and para chlorotoluenes are formed:
- The presence of AlCl3 acts as a catalyst for the chlorination reaction. It facilitates the formation of the electrophilic chlorine species that can attack the benzene ring.
- The electrophilic chlorine species can react with toluene, leading to the substitution of a hydrogen atom with a chlorine atom. This reaction can occur at the ortho (adjacent) and para (opposite) positions relative to the methyl group.
- As a result, ortho-chlorotoluene (C6H4CH3Cl) and para-chlorotoluene (C6H4CH3Cl) are formed as the major products.

c) Once a chlorine atom is introduced into the benzene ring, further chlorination at the benzene ring becomes difficult compared to the first chlorination:
- The first chlorination reaction is relatively easy because there are many available hydrogen atoms on the benzene ring for substitution.
- However, once a chlorine atom is introduced, it deactivates the benzene ring towards further chlorination. This is due to the electron-withdrawing nature of the chlorine atom, which reduces the electron density on the ring and makes it less reactive towards electrophilic attack.
- As a result, the subsequent chlorination reactions become more difficult and result in lower yields of chlorinated products.

d) Chlorination of toluene in the presence of AlCl3 is more difficult than benzene:
- Toluene is more reactive towards chlorination compared to benzene due to the presence of the methyl group.
- The methyl group is an electron-donating group, which increases the electron density on the benzene ring and makes it more susceptible to electrophilic attack.
- The presence of AlCl3 as a catalyst enhances the reactivity of toluene towards chlorination, making it easier to chlorinate toluene compared to benzene.