Particle A with charge $Q$ and particle B with charge $2 Q$ are fixed at positions $\vec{r}_A$ and $\vec{r}_B$, respectively. The force on $A$ due to $B$ is $\vec{F}_{B A}$, and that on $B$ due to $A$ is $\vec{F}_{A B}$. Which of the following options is correct?

Two uniformly charged concentric thin spherical shells of radii $r_1$ and $r_2$ have charges $+Q$ and $-Q$, respectively. How does the electrostatic potential vary with distance from the center of the shells?

Consider a very long cylinder of radius $a$ having a uniform positive charge density $\rho$. A sphere of radius $a$ has been carved out (see figure), leaving no charge in that region. The distance radially outward to the cylinder, as measured from the center of the sphere is $x$. At what value of $x$ will the electric field be maximum?

A conducting sphere of radius $a$ initially contains a uniform volume charge density $\rho$. What is the electric flux $\Phi$ through a spherical surface of radius $2 a$ centered at a point on the surface of the charged sphere (see figure) at a later time $t$ ? ( $\epsilon_0$ is the permittivity of free space.)