An electrical element x connected to an alternating voltage source has current through it leading the voltage by $\frac {\pi}{2}$ radius. Identify x and write an expression for its reactance.
(a) $C\omega$
(b) $\frac {C}{\omega}$
(c) $\frac {\omega}{C}$
(d) $\frac {1}{C\omega}$