$HBr$ and NBS combine to form a low concentration of $B{r}_2,$ which is used in the next step of the mechanism. Add curved arrows to show the second propagation step, which forms the monohalogenated product.

Hint

Attempts: $1$ of $1$ used

Step $4$

Identify the correct explanation for why only one product is formed.

The benzylic bromide is the most stable product possible.

The hydrogen atoms in the ring can be abstracted to generate a radical which doesn't involve in resonance.

The hydrogen atoms in the ring can be abstracted to generate a resonance$-$stabilized radical.

The benzylic hydrogen atom is the only hydrogen atom that can be abstracted to generate a resonance$-$stabilized radical.