Answer-Small bubbles are perfectly spherical because of –

Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer.In the absence of other forces, including gravity, drops of virtually an liquids would be perfectly spherical. The spherical shape minimizes the necessarywall tensionof the surface layer according to Laplaces law.