$A$ disk of radius $a/4$ having a uniformly distributed charge $6 \text{ C}$ is placed in the $x-y$ plane with its centre at $(-a/2, 0, 0)$. $A$ rod of length $a$ carrying a uniformly distributed charge $8 \text{ C}$ is placed on the $x$-axis from $x = a/4$ to $x = 5a/4$. Two point charges $-7 \text{ C}$ and $3 \text{ C}$ are placed at $(a/4, -a/4, 0)$ and $(-3a/4, 3a/4, 0)$,respectively. Consider a cubical surface formed by six surfaces $x = \pm a/2, y = \pm a/2, z = \pm a/2$. The electric flux through this cubical surface is
- A
$\frac{-2 \text{ C}}{\varepsilon_0}$
- B
$\frac{2 \text{ C}}{\varepsilon_0}$
- C
$\frac{10 \text{ C}}{\varepsilon_0}$
- D
$\frac{12 \text{ C}}{\varepsilon_0}$