The least value of form factor is for the Square wave.

Explanation:

1. Form Factor:
The form factor of a waveform is a measure of how closely the waveform resembles a perfect sinusoid. It is the ratio of the RMS value of the waveform to its average value.

2. Sinusoidal Wave:
A sinusoidal wave is a waveform that represents a perfect sinusoid. It has a smooth and continuous curve with no abrupt changes. The ratio of the RMS value to the average value for a sinusoidal wave is √2. Therefore, the form factor for a sinusoidal wave is √2.

3. Square Wave:
A square wave is a waveform that alternates between two constant amplitude levels. It has abrupt changes from one level to another. The ratio of the RMS value to the average value for a square wave is 1. Therefore, the form factor for a square wave is 1.

4. Triangular Wave:
A triangular wave is a waveform that ramps up and down linearly between two amplitude levels. It has smooth and continuous changes, but not as smooth as a sinusoidal wave. The ratio of the RMS value to the average value for a triangular wave is 1.155. Therefore, the form factor for a triangular wave is 1.155.

5. Sawtooth Wave:
A sawtooth wave is a waveform that ramps up linearly and then abruptly drops back to the starting level. It has abrupt changes similar to a square wave. The ratio of the RMS value to the average value for a sawtooth wave is 1.155. Therefore, the form factor for a sawtooth wave is 1.155.

Conclusion:
Among the given options, the square wave has the least value of form factor, which is 1. Therefore, option 'B' (Square) is the correct answer.