Which of the following is a correct statement?

$A$ metallic spherical shell has an inner radius $R_1$ and outer radius $R_2$. $A$ charge $Q$ is placed at the centre of the spherical cavity. What will be the surface charge density on the inner surface?

In a region,the electric field is given by $\overrightarrow{E}=(3 \hat{i}+5 \hat{j}+7 \hat{k}) \text{ NC}^{-1}$. The electric flux through a surface of area $3 \text{ m}^2$ in the $yz$-plane is (in $SI$ units):

Consider an electric field $\vec{E} = 3 \times 10^3 \hat{i} \text{ N/C}$. What is the flux through a square of side $10 \text{ cm}$ in $Nm^2/C$ if the normal to its plane makes a $60^\circ$ angle with the $X$-axis?

The electric field in a region is given by $\overrightarrow{E} = (\frac{3}{5} E_{0} \hat{i} + \frac{4}{5} E_{0} \hat{j}) \, N/C$. The ratio of the flux of this field through a rectangular surface of area $0.2 \, m^{2}$ (parallel to the $y-z$ plane) to that through a surface of area $0.3 \, m^{2}$ (parallel to the $x-z$ plane) is $a : b$,where $a = \dots$ [Here $\hat{i}, \hat{j}$ and $\hat{k}$ are unit vectors along the $x, y$ and $z$-axes respectively].

If a charge $Q$ is placed at the corner of a cube,what is the electric flux passing through one of its faces?