The correct answer is: C. r.m.s. value of current is less than average value.
The root mean square (rms) value of a waveform is the square root of the average of the squares of the instantaneous values of the waveform. The average value of a waveform is the sum of the instantaneous values of the waveform divided by the number of values.
For a square waveform, the rms value is equal to 0.707 times the average value. This is because the square waveform is symmetrical about the horizontal axis, so the positive and negative half-cycles are equal in magnitude. The average value of a square waveform is equal to half the peak value.
Therefore, the rms value of a square waveform is less than the average value.