Answer
$2C$
Work Step by Step
The best way to solve this problem is graphically, as we see in the figure below.
Noting that $C_1=C_2=C_3=C_4=C_5=C_6=C$.
It is obvious that the right arrangement is easier to figure out than the left, so we will continue with the right one.
There are no current passes through $C_5$ since $V_3-V_4=0$.
Also note that the bottom 5 capacitors will make a balanced Wheatstone bridge circuit and the equivalent capacitance is $C$.
Hence the net equivalent capacitance is $2C$.
$$\boxed{C_{eq}=2C}$$
