Correct Answer - Option 4 : 0.866

__Concept:__

Pitch factor for nth harmonic is given by,

\({k_c} = \cos \frac{{n\alpha }}{2}\)

Where α is short pitch angle in degrees

__Calculation:__

Given that, short pitch angle (α) = 60°

Pitch factor = cos (60/2) = cos 30 = 0.866