CBSE Class 12-science Answered

since gauss law  work greatly  for symmetrical surfaces. generally we have mainly three  symmtries

1- for solid sphere  or spherical shell we take concentric sphere as a gaussian surface.

2- for infinite line charge we take a coaxial cylinder as a gaussian surface.

3- for infinite plane sheet, we take gaussian pill box as a gaussian surface.

As such a gaussian surface can have any shape, as long as it encloses the charge. The only reason for choosing a symmetric surface is to make integration, required for finding flux, easier.