Introduction:
Sulphonation is a chemical reaction in which a sulfonyl group (-SO3H) is introduced into a molecule. It is commonly used to introduce sulfonic acid groups into organic compounds. Not all compounds can be easily sulphonated, as it depends on the presence of certain functional groups or the reactivity of the molecule. Among the given options, toluene is the compound that can be most readily sulphonated.

Explanation:
Benzene:
Benzene is a highly stable compound due to its aromaticity. It does not readily undergo sulphonation because the electron density in benzene is evenly distributed over the entire ring, making it difficult for the electrophilic sulfonylating agent to attack the benzene ring. Therefore, benzene is less reactive towards sulphonation.

Nitrobenzene:
Nitrobenzene has a nitro group (-NO2) attached to the benzene ring. Nitro groups are electron-withdrawing groups, which decrease the electron density on the benzene ring, making it slightly more reactive than benzene. However, the reactivity of nitrobenzene towards sulphonation is still lower compared to toluene.

Chlorobenzene:
Chlorobenzene has a chlorine atom (-Cl) attached to the benzene ring. Chlorine is a weak electron-withdrawing group, which slightly decreases the electron density on the benzene ring. This makes chlorobenzene more reactive than benzene but less reactive than toluene towards sulphonation.

Toluene:
Toluene has a methyl group (-CH3) attached to the benzene ring. The methyl group is an electron-donating group, which increases the electron density on the benzene ring. This makes toluene more reactive towards sulphonation compared to benzene, nitrobenzene, and chlorobenzene. The increased electron density facilitates the attack of the electrophilic sulfonylating agent, leading to the formation of the sulphonated product.

Therefore, among the given options, toluene is the compound that can be most readily sulphonated.

Toulene is para and ortho directing . It activates the ring towards the sulphonation reaction in comparison to -Cl group and -NO2 group which deactivate the ring. toulene can be more easily attacked in comparison to benzene because of the presence of electron donating group.