The $S.I.$ unit of electric flux is

$A$ charge $q$ is placed at the centre of the base of a cubical box of side $a$ with the top open. The flux of the electric field through the open surface is not considered,but the flux through the remaining five surfaces of the cubical box is:

$A$ hollow cylinder has a charge $q$ at its center. If $\phi$ is the electric flux associated with the curved surface $B,$ the flux linked with the plane surface $A$ will be $:-$

Two point charges $8 \mu \text{C}$ and $-2 \mu \text{C}$ are located at $x = 2 \text{ cm}$ and $x = 4 \text{ cm}$, respectively on the $x$-axis. The ratio of electric flux due to these charges through two spheres of radii $3 \text{ cm}$ and $5 \text{ cm}$ with their centers at the origin is . . . . . . .

An infinitely long uniform line charge distribution of charge per unit length $\lambda$ lies parallel to the $y$-axis in the $y-z$ plane at $z=\frac{\sqrt{3}}{2} a$ (see figure). If the magnitude of the flux of the electric field through the rectangular surface $A B C D$ lying in the $x-y$ plane with its center at the origin is $\frac{\lambda L }{ n \varepsilon_0}$ (where $\varepsilon_0$ is the permittivity of free space),then the value of $n$ is

$A$ sphere of radius $R$ and charge $Q$ is placed inside an imaginary sphere of radius $2R$ whose center coincides with the given sphere. The flux related to the imaginary sphere is