Answer
$C_{eq}=\frac{1}{C_1}+\frac{1}{C_2}+\frac{1}{C_3}$
Work Step by Step
If the capacitors are connected in series then equivalent capacitance is the sum of the reciprocals of the individual capacitance of the capacitors.
So, equivalent capacitance of three capacitors in series is given as
$C_{eq}=\frac{1}{C_1}+\frac{1}{C_2}+\frac{1}{C_3}$
