A bomb explodes on the moon. How long will it take for the sound to reach the earth?

Sound waves are mechanical waves that need an elastic medium to propagate. In the space between the moon and the earth, there is no medium (solid, liquid, or gas). Sound is created in the medium particle due to vibrations, that is, it requires some medium for propagation and the moon has no atmosphere.
Therefore, one will never listen to the sound of the blast occurring on the moon.