Domain: Natural Science — Chemistry
Target concept: The electrolytic cell exhibits a faster bubble formation rate after the addition of a supporting electrolyte.

Video generation prompt: Two identical transparent electrolytic cells are placed side by side, each containing water and metal electrodes connected to the same power supply; potassium nitrate is added to the right cell, while the left cell remains unchanged.

Evaluation guide:
(i) Target concept: Supporting electrolytes enhance electrical conductivity in aqueous electrolysis, thereby increasing the rate of electrochemical gas evolution (H₂/O₂) at electrodes.
Minimum mechanism: Water must undergo electrolysis (2H₂O → 2H₂ + O₂); presence of inert, soluble electrolyte (KNO₃) must increase ionic strength without participating in redox reactions; increased current density at fixed voltage must drive faster bubble nucleation and detachment.
(ii)Storyline: [Frame 0–2] Static wide shot: two identical transparent cells side-by-side, each with submerged metal electrodes, both wired to single power supply; left cell contains only water; right cell receives addition of KNO₃ (solid crystals dissolving or clear solution poured). [Frame 3–4] Power is switched on (visible indicator or wire glow not required, but bubbling onset marks timing). [Frame 5–10] Bubbles emerge from electrode surfaces: right cell shows immediate, dense, frequent bubbling; left cell shows delayed, sparse, infrequent bubbling; both cells remain fully visible in fixed frame; no occlusion, no camera motion; all phenomena occur within electrode-water interface zone.

Manual:
Experimental Procedure
1. Place two identical transparent electrolytic cells side by side.
2. Fill both with pure water and insert identical metal electrodes.
3. Connect both cells to the same DC power supply.
4. Add solid potassium nitrate only to the right cell.
Observation of Experimental Phenomena
After power is applied, bubbles form continuously on electrodes in both cells, but bubble formation begins earlier and occurs at a visibly higher frequency in the right cell than in the left cell.
Summary of Experimental Principles
Potassium nitrate acts as a supporting electrolyte, increasing solution conductivity and enabling faster ion migration and electrochemical reaction kinetics at the electrodes, resulting in accelerated gas evolution (bubbling).

Prompt Grounding rubric:
level_1: Neither transparent electrolytic cell is visible, or only one of the two cells appears; no metal electrodes are visible in either cell; no shared power supply connects the cells; no addition of potassium nitrate (or any substance) is shown entering either cell; the left and right cells look identical with no way to tell which one received the addition.
level_2: Both cells appear together, but at least one lacks visible metal electrodes, or the two cells are not wired to one common power supply (e.g., separate supplies, or no visible wiring at all); an addition event occurs, but it is unclear which cell receives it, or the added material does not read as a solid or solution being introduced into the water.
level_3: Two visually matching transparent cells sit together, each holding water with a pair of metal electrodes submerged and wired to one shared power supply; the right cell receives a clear addition event (crystals or solution poured in) while the left cell receives nothing; the identity of the added substance as potassium nitrate specifically is not established (e.g., no crystal color or dissolving cue distinguishing it from plain water).
level_4: All of score 3, AND the right-cell addition is visually identifiable as a white crystalline solid or a clear solution added only to that cell, while the left cell shows no addition event at any point; the two electrode pairs match each other in shape and size; the shared power supply's two output leads can each be traced to one cell.
level_5: All of score 4, AND the addition event stays confined to the right cell, with no crystals, splashes, or residue reaching the left cell; electrodes in both cells are identical rods or plates positioned symmetrically; the camera holds one fixed, front-on framing that keeps both complete cells in view for the whole clip, with nothing overlapping or hiding either cell.

Scientific and Causal Correctness rubric:
level_1: Bubbles form at the same rate in both cells despite the potassium nitrate addition, or bubbles appear in the untreated left cell before they appear in the right cell, or bubbles emerge from the container walls or water surface rather than from the electrode surfaces.
level_2: Bubbling starts in both cells at visibly the same moment and pace regardless of the potassium nitrate addition, or bubbles appear in one cell before any power is applied, showing no dependence on the electrolysis current.
level_3: Once power is applied, both cells bubble at their electrodes, and the right cell (with potassium nitrate) visibly produces bubbles more often per unit time than the left cell; the left cell's bubbling visibly lags behind the right cell's once both have started, and no bubbles originate anywhere except the electrode surfaces.
level_4: All of score 3, AND the right cell's faster bubbling is visible from the earliest moments after power-on (bubbles appear sooner there and build up more quickly than in the left cell); the left cell's bubbling stays visibly slower and sparser the entire time, never catching up to the right cell's pace.
level_5: All of score 4, AND the rate gap holds for the entire clip: the right cell shows many bubbles releasing from its electrodes at once in a near-continuous stream, while the left cell shows only occasional single bubbles with longer gaps between them; at no point does the left cell bubble as fast as or faster than the right cell.

Spatiotemporal Consistency rubric:
level_1: A cell or an electrode jumps to a new position between frames instead of staying put; a power-supply wire disappears and reappears; one of the two cells vanishes for part of the clip; a bright reflection or shadow flips to the opposite side of a cell from one frame to the next with no cause; a cell's transparent wall flickers between clear and opaque or visibly warps out of its rigid shape.
level_2: An electrode wobbles or drifts more than the light jostling a rising bubble would cause; a container edge appears to ripple or bend; the two cells catch light differently from one moment to the next; bubbles suddenly stall mid-rise and then jump forward.
level_3: Both cells, their electrodes, and the shared power supply stay in the same place and orientation for the whole clip; nothing swaps position or briefly disappears; the lighting stays even with no shadow jump or flicker; bubbles rise smoothly without stalling or jumping.
level_4: All of score 3, AND bubbles trace a gently curving upward path rather than darting sideways; the water surface in each cell stays level and undisturbed by the potassium nitrate addition or by the bubbling itself; the two cells keep the same spacing between them with no camera drift; there is no jump cut or freeze-frame anywhere in the clip.
level_5: All of score 4, AND individual bubbles stay clearly countable and located as they rise, with no smeared or streaking motion trail swallowing them up; the cell walls do not warp or bend the view of the electrodes behind them; every bubble's rise and detachment reads as ordinary fluid motion at this scale, with no sudden speed changes.