3, 5 - Dibromotoluene can be best synthesised by

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Explanation

To synthesize 3,5-dibromotoluene, we can follow these steps:

### Step-by-Step Solution:

1. **Starting Material**: Begin with toluene (C6H5CH3), which has a methyl group (CH3) attached to the benzene ring. The structure can be represented as follows:
\[ \text{C6H5-CH3} \]

2. **Electrophilic Substitution Reaction**: Use aniline (4-methyl aniline) as a starting point. The lone pair on the nitrogen of aniline will activate the benzene ring towards electrophilic substitution. The reaction with bromine (Br2) in the presence of water (H2O) will lead to the substitution of bromine atoms at the ortho and para positions relative to the amino group. However, due to steric hindrance, the substitution will predominantly occur at the ortho position.

3. **Formation of 3-Bromo-4-Methyl Aniline**: The product after bromination will be 3-bromo-4-methyl aniline, which can be represented as:
\[ \text{C6H5-CH3-Br} \]

4. **Diazotization**: Treat the amine group (NH2) with nitrous acid (HNO2) to convert it into a diazonium salt. This step involves the formation of a diazonium ion (C6H5-CH3-N2^+).

5. **Substitution with Bromine**: The diazonium salt can then be treated with CuBr, which will replace the diazonium group with a bromine atom, leading to the formation of 3,5-dibromotoluene.

6. **Final Product**: The final product will be 3,5-dibromotoluene, represented as:
\[ \text{C6H3(Br)2-CH3} \]

### Conclusion:
The best synthesis route for 3,5-dibromotoluene is through the reaction of 4-methyl aniline with bromine followed by diazotization and substitution with CuBr.