Explanation: The no-load voltage ratio of a power transformer is fundamentally determined by its **turns ratio**. Transformers operate on the principle of mutual induction. When an alternating voltage is applied to the primary winding, it creates a continuously changing magnetic flux in the core. This flux links both the primary and secondary windings. According to Faraday's Law of Induction, the voltage induced in each winding is directly proportional to the number of turns in that winding, for a given rate of change of magnetic flux. Therefore, the ratio of the primary voltage to the secondary voltage is essentially equal to the ratio of the number of turns in the primary winding to the number of turns in the secondary winding (Vp/Vs = Np/Ns). This relationship holds true at no-load because there is minimal current in the secondary, and thus negligible voltage drop due to winding resistance or leakage reactance. * **A) Power ratio:** An ideal transformer has a power ratio of approximately 1:1 (power in equals power out, minus losses). This does not determine the voltage transformation. * **C) Voltage ratio:** This is what the question asks to determine, not a factor that determines it. * **D) Power factor:** Power factor relates to the phase angle between voltage and current in a circuit. While important for understanding load performance, it does not determine the transformer's inherent no-load voltage transformation capability, which is a structural property.