In a parallel circuit, the voltage across each branch is the same, and the branch current follows I = V/R. If you double the resistance of one branch while the supply voltage stays fixed, that branch’s current becomes I' = V/(2R) = (1/2)(V/R). So the current in that branch is halved. The other branches see the same voltage and are unaffected by this change in the first branch, though the total current drawn from the source would decrease accordingly.

Resistance in a metal comes from electrons colliding with the lattice ions and losing energy as heat. In a longer wire, electrons must travel a greater distance, so they encounter more ions along the way. Each collision transfers some electric energy to the lattice, so the total energy lost per unit charge increases with length. That’s why resistance grows with length (and, for a given material, is proportional to L and inversely proportional to cross-sectional area, R = ρL/A). The idea that the longer path means more collisions with ions is the precise reason the resistance is higher. The other ideas—changes in material along the length or the wire simply being heavier—don’t explain the electrical resistance in the same direct way.

In a single-loop series circuit, Kirchhoff’s voltage law applies: the sum of all voltage drops around the loop must equal the supply voltage. The battery provides a fixed total potential difference, and as the same current flows through every component, the voltage across each component adds up to that same total. In other words, the sum of the potential differences across all components equals the battery’s total potential difference. The current and the resistance explain how that voltage is distributed (V = IR tells you how much drop each component gets for the given current), but the fundamental idea here is that voltages around the loop add up to the source voltage.

Light affects how well the material conducts electricity. An LDR is a semiconductor whose conductivity rises when illuminated. When bright light shines on it, photons generate more free charge carriers (electrons and holes), so the material conducts better. For a given applied voltage, more current flows, which means the resistance drops. It isn’t literally zero or infinite in normal conditions, but it becomes much lower than in darkness. That’s why the correct choice is that the resistance is low in bright light.