As shown in the figure, a point charge Q is placed at the centre of conducting spherical shell of inner radius a and outer radius b. The electric field due to charge \mathrm{Q} in three different regions \mathrm{I}, \mathrm{II} and \mathrm{III} is given by:
(\mathrm{I}: r < a, \mathrm{II}: a < r < b, III: r>b )