<span>When a molecule absorbs a photon, one of its electrons is raised to the excited state</span>
2Na + Br2 -> 2NaBr
Br is a diatomic element so the 2 is a subscript, not a coefficient.
I believe it would be both ? if you can choose that. Basically decomposition is the process of decaying or breaking down, so obviously at some point it would make a physical change. But it would also change chemically!