Question

when we fill any liquid in a container to its brim we can see the shape of water at the surface is like a dome and not flat . why does this happens

Answer 1

This happens because of the property of water called surface tension.
Surface tension can be defined as the tension on the surface of a liquid due to the cohesive force(There is a intermolecular force of attraction in any liquid which is called cohesive force) on the molecules of the surface. Because of this tension on the surface , the free surface of water tends to contract so as to occupy a minimum surface area at rest so as to reduce the surface tension to maximum possible value and as such it looks like dome shaped.