Right option is (b) Kn = \(\frac{V_{p(rated)}}{V_{s(rated)}}\)
Easiest explanation: In a potential transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary voltage to the magnitude of the actual secondary voltage.
where, R is the transformation ratio
Vp(rated) is the rated primary winding voltage
Vs(rated) is the rated secondary winding voltage.