A sine wave has a frequency of 50 Hz. Its angular frequency is __________ radian/second.

100 n
50 jt
25 JT
5 n

The correct answer is $\boxed{\text{C}}$, 25 $\pi$ rad/s.

The angular frequency is the number of radians that a sine wave goes through in one second. It is denoted by $\omega$ and is given by the formula:

$$\omega = 2\pi f$$

where $f$ is the frequency in Hz.

In this case, the frequency is 50 Hz, so the angular frequency is:

$$\omega = 2\pi (50 \text{ Hz}) = 25\pi \text{ rad/s}$$