Question

how many aromatic isomer of C7H7Cl is possible. answer is given 3 but I think 4 .I think 4th one is chloromethyl benzene

Answer 1

Yes... there are 4 possible aromatic isomers.
1. Ortho chloro toulene
2. Meta chloro toulene
3. Para chloro toulene
4. Chloromethyl benzene

Answer 2

The aromatic isomers of $\mathrm{C_7H_7Cl}$ are given in the image.

Here, 7 carbon atoms are given and it is asking for aromatic isomer, hence one benzene ring should be here. Each benzene ring contains 6 carbon atoms therefore one C atom as $\mathrm{CH_3 \ or \ CH_2Cl}$ will come as side chain over benzene ring.

Overall, there will be three position isomers of chlorotoluene in which the position of Cl will come at ortho, para, and meta with respect to $\mathrm{CH_3}$ group and one will be $\mathrm{-CH_2Cl}$. So, it will be benzyl chloride.