Final answer:
The highest resistance and lowest current in a circuit occur where the switch is open, presenting a high resistance leading to no current flow. When closed, the switch adds negligible resistance, allowing current to flow through all resistors equally in a series circuit.
Step-by-step explanation:
When the switch is closed in a circuit, the resistance would be highest in the circuit with the greatest overall resistance, and the current would be lowest in that circuit. In such a case, the switch behaves as if it has nearly zero resistance when closed, which does not contribute significantly to the overall resistance of the circuit. Conversely, when the switch is open, it has an extremely large resistance, effectively becoming an open circuit, leading to no current flow.
As for which resistor the most current flows through, it would not be correct to say that the 25Ω resistor has the most current just because it has the highest resistance. Instead, in a series circuit, the same current flows through all components.
Therefore, if there were a 25Ω resistor in series with other resistors and a closed switch, it would have the same current flowing through it as the other resistors. The current is determined by the total resistance of the circuit and the voltage supplied by the battery, according to Ohm's Law (I=V/R).