The decreasing order of reactivity towards electrophilic substitution reaction of the following compounds is:i.Benzeneii.Chlorobenzeneiii.Nitrobenzeneiv.TolueneA.i > iii > iv > iiB.iv > i > iii > iiC.iv > i > ii > iiiD.iv > ii > i > iii

The reactivity of these compounds towards electrophilic substitution reactions generally follows the order of electron-donating and electron-withdrawing groups on the benzene ring. Here's the decreasing order of reactivity:

Toluene (iv) - Toluene is the most reactive among the given compounds because it has a methyl group (-CH3) attached to the benzene ring, which is an electron-donating group. This group increases the electron density on the benzene ring, making it more reactive toward electrophilic substitution reactions.

Benzene (i) - Benzene is the next in reactivity because it is the simplest compound in the list with no substituents. It is more reactive than chlorobenzene and nitrobenzene due to its higher electron density compared to the latter two.

Chlorobenzene (ii) - Chlorobenzene is less reactive than benzene because it has a chlorine atom (-Cl) attached to the benzene ring, which is a weak electron-withdrawing group. This group decreases the electron density on the benzene ring, making it less reactive.

Nitrobenzene (iii) - Nitrobenzene is the least reactive among the given compounds because it has a nitro group (-NO2) attached to the benzene ring, which is a strong electron-withdrawing group. This group significantly decreases the electron density on the benzene ring, making it the least reactive toward electrophilic substitution reactions.

So, the correct order of reactivity is:

D. iv > ii > i > iii