Question

why there is formation of bubbles when water boils​

Answer 1

when water boils the force of attraction breaks down and the kinetic energy start to work. Due to this there is the formation of bubbles.

Answer 2

When this occurs, they form gaseous molecules of water vapor, which float to the surface as bubbles and travel into the air. Instead of air, the bubbles in a boiling pot of water are actually made up of water — it's just water in its gaseous state.