Question

Why does a balloon make a boom sound when we prick it with a pin??

Answer 1

When you inflate a balloon, the air pressure inside it is much more than the atmospheric pressure outside of it. If the balloon is pricked, all the air comes tries to come out with great force. This small hole cannot allow so much of air to go out at once. Also, now that there is weak spot in the membrane, the pressure due to the air tears apart the rubber in an instant.
Now inflate a balloon to its maximum capacity but instead of closing the opening with a knot, just hold its mouth between your thumb and forefinger preventing the air from escaping. Now if you suddenly let go of the balloon, it just moves randomly here and there but doesn't burst. This is because, the opening is large enough to allow the air to go out without the need of tearing it to make a bigger opening.