Question

When we clap sound is heard but when we clap in water sound not heard .why?

Answer 1

Sound is heard in both of the cases. Try slapping water hard with flat hand.

the nature of sound heard in both the cases will differ.

Answer 2

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.