The correct option is (d) 1
Explanation: The impedance for a series LCR circuit is given as:
Z=\(\sqrt {R^2+(X_L-X_C)^2}\) and cosΦ=\(\frac {R}{Z}\)
At resonance, XL=XC ➔ Z = R;
So, the total impedance of the circuit is only due to resistor. The phase angle between voltage and current is zero. Therefore,
Φ=0 ➔ Power factor (cosΦ)=1