The frequency of an alternating current refers to the number of complete cycles of the current that occur in one second. In this case, the frequency is stated to be 3 Hz. Hertz (Hz) is the unit used to measure frequency, and it represents the number of cycles per second.
Option 1 states that there are 6 cycles per second. This is incorrect because the given frequency is 3 Hz, not 6 Hz.
Option 2 states that there are 3 cycles per second. This is the correct answer. The frequency of 3 Hz means that there are 3 complete cycles of the current that occur in one second.
Option 3 states that there are 2 cycles per second. This is incorrect because the given frequency is stated to be 3 Hz, not 2 Hz.
Option 4 states that there is only 1 cycle per second. This is incorrect because the given frequency is stated to be 3 Hz, not 1 Hz.
Therefore, the correct answer is option 2: there are 3 cycles per second.