A plastic disc is charged on one side with a uniform surface charge density \[\sigma \]and then three quadrant of the disk are removed. The remaining quadrant is shown in figure, with V=0 at infinity, the potential due to the remaining quadrant point P is

• A. \[\frac{\sigma }{2{{\in }_{0}}}\left[ {{\left( {{r}^{2}}+{{R}^{2}} \right)}^{1/2}}-r \right]\]      
• B. \[\frac{\sigma }{2{{\in }_{0}}}\left[ R-r \right]\]
• C. \[\frac{\sigma }{8{{\in }_{0}}}\left[ {{\left( {{r}^{2}}+{{R}^{2}} \right)}^{1/2}}-r \right]\]      
• D. none of these