Question

why we cannot hear sound while we clap inside the water

Answer 1

The right one is that when you clap, the air trapped between your palms in the very impact-moment reaches supersonic speed - producing a supersonic bang. So happens when you sneeze or use a whip. (believe it or not, but the tip of a whep is moving as fast as 2 up to 3 times faster than the speed of sound in the air) 

The reason you can't hear the clap when you try to produce it under water is because water is away denser than the air, which makes sonic speed is much higher thee than it is in the air - so you'd have to be able to move your palms roughly three times faster under the water than you can in the air, which you can't do - just because the water is more dense. 

So, you can't produce a supersonic water jet; and no supersonic speed is no bang, which is you can't hear a thing! 

Remember that if you want to produce a sonic bang in some elastic medium, you need to have a piece of that medium moving supersonic!
-HOPE THIS WILL HELP U <3