Final answer:
Without additional information about the total voltage supplied or the current flowing through the circuit, it is not possible to determine the magnitude of the potential difference across the 20-ω resistor.
Step-by-step explanation:
The magnitude of the potential difference across the 20-ω resistor cannot be determined without additional information about the circuit, such as the total voltage supplied or the current flowing through the resistor. To calculate the potential difference (voltage drop) across a resistor using Ohm's Law, the formula V = IR, where V is the voltage, I is the current, and R is the resistance, can be applied. Without the current or total voltage, we cannot provide one of the multiple-choice answers given (7.8 V, 3.2 V, 5.0 V, 8.6 V, 11 V) as the correct answer to the question posed.