a
The flux passes through \(\mathrm{ABCD}(\mathrm{x}-\mathrm{y})\) plane is zero, because electric field parallel to surface. Flux of the electric field through surface \(BCGF\) \((y-z)\)

At BCGF (electric field) \(\Rightarrow \overrightarrow{\mathrm{E}}=12 \hat{\mathrm{i}}-\left(\mathrm{y}^{2}+1\right) \hat{\mathrm{j}}\)

\((x=3 m)\)

Flux \(\phi_{\mathrm{II}}=12 \times 4=48 \mathrm{Nm}^{2}{ / \mathrm{C}}\)

So \(\phi_{\mathrm{I}}-\phi_{\mathrm{II}}=0-48=-48 \mathrm{Nm}^{2}{ / \mathrm{C}}\)

\(\therefore\) Correct answer \(-48\)