Question

why do we hear sound during an explosion?

Answer 1

We can hear sound because it travels to the medium of air and brings the effect of it in our ear drum...

Answer 2

During an explosion, very high pressure is created in the air by the chemicals involved. Very quick vibrations are created.  These vibrations cause waves in air to be created and propagate them.

The waves cause high pressure and low pressure regions that are propagated in all directions through air.  These waves in air (pressure differences/vibrations) are sensed in the ear. They cause vibrations of the soft and elastic ear drum.

Those vibrations cause sensory organs to propagate signals to the brain. They are interpreted as sounds.

If an explosion happens in vacuum then we cannot hear the sound, as sound waves do not travel in vacuum.