Consider an initially neutral hollow conducting spherical shell with inner radius r and outer radius $2 \mathrm{r}$. A point charge $+\mathrm{Q}$ is now placed inside the shell at a distance $r / 2$ from the centre. The shell is then grounded by connecting the outer surface to the earth. $P$ is an external point at a distance $2 r$ from the point charge $+Q$ on the line passing through the centre and the point charge $+Q$ as shown in the figure.
The magnitude of the force on a test charge $+q$ placed at $\mathrm{P}$ will be

• A

  $\frac{1}{4 \pi \varepsilon_{0}} \frac{\mathrm{qQ}}{4 \mathrm{r}^{2}}$
• B

  $\frac{1}{4 \pi \varepsilon_{0}} \frac{9 q Q}{100 \mathrm{r}^{2}}$
• C

  $\frac{1}{4 \pi \varepsilon_{0}} \frac{4 q Q}{25 r^{2}}$
• Correct answer
  D

  0

Hence, the correct answer is option: 'D'.