When bromine reacts with methylbenzene in the presence of light (instead of a catalyst), the substitution reaction happens in the methyl group rather than the ring.
One of the hydrogen of the methyl group is replaced by a bromine atom. (chloromethyl)benzene is produced.
The reaction doesn't stop there, we can replace all the H atoms of the methyl group, but the problem asks for monosubstituted products.
So, in presence of light we can form only one product.
Answer: A. 1
