Was the Hiroshima bombing a physical or chemical change?

Answer 1

At Hiroshima, the bomb itself was a nuclear weapon. The operative word there is nuclear. Nuclear changes brought about a massive release of that nuclear energy. The nuclear energy was converted into mechanical and electromagnetic energy, which resulted in the creation of a huge amount of thermal energy.

The mechanical energy was carried outward in the blast wave. The combination of these things caused both physical and chemical changes, the latter owing to the electromagnetic and thermal (heat) energy.