The effective capacitance of the network between terminals is
(Given, C=6 μF )
CPCS=CQCT=CC=1
So, this means the given circuit is balanced Wheatstone bridge.
Now let's redraw the above circuit, considering balanced Wheatstone bridge
Since, both upper and lower branch is in series, so effective capacitance of both part will be
C′eq=C×CC+C=C2
Since both C/2 capacitors are in parallel , So effective capacitance will be
Ceq=C2+C2=C=6 μF
Hence, option (a) is correct.