1. The problem statement, all variables and given/known data: 2. Relevant equations: A conductor is an equipotential surface. The charge density near a conductor is proportional to the electric field. Electric field is the negative gradient of potential and thus electric field is in a direction normal to the surface. 3. The attempt at a solution: Since electric field is the gradient of potential, if the surface of a conductor has sharp turns, the gradient will be undefined (cannot draw a tangent plane at such points) and thus the charge density is undefined. So I think it is option (a). Am I right? Thanks.