Arrange the following in increasing order of reactivity towards sulphonation with fuming sulphuric acid.
Benzene, toluene, methoxy benzene, chlorobenzene.

Explanation

To solve the problem of arranging benzene, toluene, methoxybenzene, and chlorobenzene in increasing order of reactivity towards sulfonation with fuming sulfuric acid, we need to consider the effects of substituents on the aromatic ring. Here’s a step-by-step solution:

### Step 1: Understand the Reaction
Sulfonation is an electrophilic substitution reaction where a sulfonyl group (–SO3H) is introduced into the aromatic ring. The reactivity of the aromatic compounds towards sulfonation depends on the nature of the substituents present on the ring.

### Step 2: Identify the Nature of Substituents
- **Benzene**: No substituents, baseline reactivity.
- **Toluene**: Contains a methyl group (–CH3), which is an electron-donating group. This increases the reactivity towards electrophiles.
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