Referring to fig. the effective capacitance between A and B will be

The upper two condensers of capacities 3 μF and 6 μF are in series. Their resultant capacitance C' will be1C′=13+16=36=12 or C′=2μFSimilarly, the lower two condensers of capacities 2 μF and 2 μF are in series. Their resultant capacitance C' will be1C′′=12+12=1  or  C′′=1μFThe effective capacitance between A and B will beC=C′+C′′=2+1=3μF