Shown in the figure are two point charges $+Q$ and $-Q$ inside the cavity of a spherical shell. The charges are kept near the surface of the cavity on opposite sides of the centre of the shell. If $\sigma_1$ is the surface charge density on the inner surface and $Q_1$ is the net charge on it,and $\sigma_2$ is the surface charge density on the outer surface and $Q_2$ is the net charge on it,then:

• A
  $\sigma_1 \neq 0, Q_1 = 0; \sigma_2 = 0, Q_2 = 0$
• B
  $\sigma_1 \neq 0, Q_1 = 0; \sigma_2 \neq 0, Q_2 = 0$
• C
  $\sigma_1 = 0, Q_1 = 0; \sigma_2 = 0, Q_2 = 0$
• D
  $\sigma_1 \neq 0, Q_1 \neq 0; \sigma_2 \neq 0, Q_2 \neq 0$