An alternating current has a frequency has a frequency of 50Hz. How many times does it change its direction in one direction?

Question

$\begin{array}{1 1} (a)\; \text{50 times per second} \\ (b)\; \text{25 times per second} \\ (c)\; \text{100 times per second} \\ (d)\; \text{200 times per second} \end{array}$