To sense dark conditions with an LDR, where should it be positioned?

Positioning the light-dependent resistor (LDR) in the R2 position is appropriate for sensing dark conditions because it typically allows the resistance of the LDR to influence the output of the circuit. The LDR's resistance decreases in light and increases in darkness. When the LDR is connected in this manner, as ambient light decreases (or it becomes dark), the resistance of the LDR increases, which can lead to a change in voltage detected by the circuit. This configuration is often used in voltage divider circuits, where the output voltage can be measured to determine the light level effectively.

The other options are less suitable for achieving the desired effect in sensing dark conditions. For example, placing the LDR in the R1 position might not adequately influence the voltage across the output, as it would primarily be affected by variations in the other component. Connecting it in series with a battery doesn’t allow for measuring light levels since it would not provide a varying output voltage based on light conditions. Lastly, putting it in parallel with the output would complicate the circuit behavior and wouldn't effectively allow for the necessary voltage changes to determine light levels.