(i)

The first transformation is Methyl benzoate from benzene. The following transformation can be achieved in five steps.

In the first step, benzene reacts with Br₂ in the presence of FeBr₃ , and bromobenzene is obtained as a product. The reaction is an example of an electrophilic aromatic substitution reaction. 

In the second step, bromobenzene reacts with Mg and the Grignard reagent is obtained. In the third step, the Grignard reagent gives a nucleophilic addition reaction with CO₂ followed by acidification(4th step), hence benzoic acid is obtained as a product. 

In the last step, benzoic acid reacts with methanol in an acidic medium and gives ester as a product. 

All reactions are as follows:

(ii)
The second transformation is m-Nitrobenzoic acid from benzene. The following transformation can be achieved in five steps.

In the first step, benzene reacts with Br₂ in the presence of FeBr₃ , and bromobenzene is obtained as a product. The reaction is an example of an electrophilic aromatic substitution reaction. 

In the second step, bromobenzene reacts with Mg and the Grignard reagent is obtained. In the third step, the Grignard reagent gives a nucleophilic addition reaction with CO₂ followed by acidification(4th step), hence benzoic acid is obtained as a product. 

In the last step, benzoic acid undergoes a nitration reaction reacts with nitric acid and sulphuric acid and gives
meta-​nitrobenzoic acid. 

The reactions are as follows:

 

(iii)
The third transformation is p-Nitrobenzoic acid from benzene. The following transformation can be achieved in more than one step:

In the first step, benzene reacts with methyl chloride in the presence of anhyd. AlCl₃ , and toluene is obtained as a product. The reaction is an example of an electrophilic aromatic substitution reaction. 

In the second step, toluene undergoes a nitration reaction when reacts with nitric acid and sulphuric acid. The nitration occur at the para and ortho position because -CH₃ is ortho para directing. 

Then p-nitrotoluene undergoes an oxidation reaction followed by acidification. The product obtained is p-nitrobenzoic acid. 

The reactions are as follows:

(iv)
The fourth transformation is phenylacetic acid from benzene. The following transformation can be achieved in more than one step:

In the first step, benzene reacts with methyl chloride in the presence of anhyd. AlCl₃ , and toluene are obtained as a product. The reaction is an example of an electrophilic aromatic substitution reaction. 

In the second step, toluene reacts with Br₂/hv, and benzyl bromide is obtained as a product. The reaction follows the free radical substitution reaction. 

In the third step, benzyl chloride undergoes a nucleophilic substitution reaction. In this reaction, benzyl chloride reacts with KCN, and benzyl cyanide is obtained as a product.

In the last step, benzyl cyanide undergoes a hydrolysis reaction in an acidic medium and phenylacetic acid is obtained as a product.  

The reactions are as follows:
 

(v)

The fIfth transformation is p-nitrobenzaldehyde. from benzene. The following transformation can be achieved in more than one step:

In the first step, benzene reacts with methyl chloride in the presence of anhyd. AlCl₃ , and toluene are obtained as a product. The reaction is an example of an electrophilic aromatic substitution reaction.  

In the second step, toluene undergoes a nitration reaction when reacts with nitric acid and sulphuric acid. The nitration occurs at the para and ortho position because -CH₃ is ortho para directing. 

In the third step, p-nitrotoluene undergoes an oxidation reaction, and the CH₃ group is converted into the CHO group. The reaction is an example of an Etard reaction. 

In this reaction, p-nitrotoluene reacts with chromyl chloride and a methyl group oxidized to a chromium complex, which on hydrolysis gives corresponding benzaldehyde.

The reactions are as follows: