Please answer it soon please

Dear student,

All the dielectrics are in series
$$\begin{gathered} C\text{'} =\frac{k_1\epsilon (A/3)}{d}+\frac{k_2\epsilon (A/3)}{d}+\frac{k_3\epsilon (A/3)}{d} =\frac{(k_1+k_2+k_3)\epsilon A}{3d} \\ so C\text{'} =\frac{C(k_1+k_2+k_3)}{3} =\frac{(2.1+3.6+4.5)}{3} =3.4 C \end{gathered}$$

Option 1 is correct

Regards