Two 0.68 µF capacitors are connected in series across a 10 kHz sine wave signal source. The total capacitive reactance is

Answer: Option A

Capacitive Reactance should be:
$${\text{X}}_{\text{C}}=\frac{1}{2}\pi \text{fC}$$
Where:
f = frequency
C = Capacitance
For capacitors in series:
$$\begin{array}{rl}& \frac{1}{\text{C}}=\frac{1}{{\text{C}}_1}+\frac{1}{{\text{C}}_2}\\ & \text{So,}\text{C}=3.4\times 10^{-7}\text{F}\\ & \text{So:}\\ & {\text{X}}_{\text{C}}=\frac{1}{2\pi \cdot 3.4\times {10}^{-7}\cdot 10000}=46.8\Omega \end{array}$$