Answer:
Nil
Step-by-step explanation:
Sound is a wave whose speed depends on the medium it is traveling in. Sound wave travel faster in water as compared to air. In water the speed of sound wave is around 1480 m/sec whereas in air it is around 343 m/sec.
Since Nil is underwater he will hear the sound of the explosion first. But, the quality of sound will be better for John. This is because humans have evolved to listen in the air and not water. So the sound will not be clear to Nil underwater.