The correct answer is (b) \(\frac{1.11V_A}{V_B}\)
For explanation I would say: Form factor of the wave = \(\frac{RMS \,value}{Mean \,value}\)
Moving iron instrument will show rms value. Rectifier voltmeter is calibrated to read rms value of sinusoidal voltage that is, with form factor of 1.11.
∴ Mean value of the applied voltage = \(\frac{V_B}{1.11}\)
∴ Form factor = \(\frac{V_A}{V_B/1.11} = \frac{1.11V_A}{V_B}\).