Correct Answer - Option 2 :

4%
Concept:

In a 3-phase induction motor, the synchronous speed can be calculated as

\({N_s} = \;\frac{{120f}}{P}\)

\(s = \;\frac{{{N_s} - {N_r}}}{{{N_s}}}\)

Where, Ns = Synchronous speed in rpm,

Nr = Rotor speed in rpm,

s = Slip of the machine,

f = Supply frequency in Hz,

P = Number of poles,

Calculation:

\({N_s} = \frac{{120 \times 50}}{6} = 1000\;rpm\)

\(s = \frac{{1000 - 960}}{{1000}} = 0.04\)