Domain: Natural Science — Marine Science
Target concept: Carbon dioxide bubbles are introduced into seawater containing a pH indicator until the color reaches a stable state.

Video generation prompt: In a transparent aquarium filled with seawater and a pH indicator dye, carbon dioxide was introduced as bubbles through a diffuser at the bottom, and then the supply of carbon dioxide was subsequently closed.

Evaluation guide:
(i) Target concept: Acidification of seawater via dissolved CO2 induces measurable, visible pH-dependent color change in indicator dye.
Minimum mechanism: CO2 must dissolve to form H2CO3 (requiring aqueous medium, gas-liquid interface, and time for equilibration); indicator must be chemically stable and responsive in the relevant pH range; color change must reflect protonation state, not oxidation or photolysis.
(ii)Storyline: [Phase 1: Baseline] Fixed-view shot shows full aquarium with still, uniformly blue liquid and inert bottom diffuser. [Phase 2: Initiation] Bubbles emerge continuously from diffuser; no color change yet. [Phase 3: Transition] Color begins shifting uniformly from blue → green → yellow/orange as bubbles persist. [Phase 4: Stabilization] Color reaches and holds stable yellow/orange while bubbles continue. [Phase 5: Termination] CO2 supply closes → bubbles cease completely → color remains fixed (no fade/reversion). All phases occur sequentially in same scene, no occlusion, no viewpoint shift, and liquid volume remains constant.

Manual:
Experimental Procedure
1. Fill transparent aquarium with seawater and add pH indicator dye (e.g., bromothymol blue) until liquid appears uniformly blue.
2. Insert CO2 diffuser at aquarium bottom and begin bubbling CO2 steadily.
3. Observe color shift as bubbles rise and dissolve; wait until color stabilizes to yellow/orange.
4. Close CO2 supply — bubbles cease immediately.
Observation of Experimental Phenomena
- Initial liquid color: uniform blue or purple.
- During bubbling: continuous upward bubble stream from bottom diffuser; liquid color transitions uniformly through green to stable yellow/orange.
- After CO2 closure: bubbles fully stop; final color remains stable yellow/orange with no reversal.
Summary of Experimental Principles
CO2 dissolves in seawater to form carbonic acid (H2CO3), lowering pH; pH indicator dye changes color reversibly across pH range — blue (pH >7.6), green (pH ~7.0), yellow/orange (pH <6.0).

Prompt Grounding rubric:
level_1: No transparent aquarium is visible; no seawater-like liquid is shown; no pH indicator dye is visible; no CO2 diffuser is shown at the bottom; no bubble generation is observed; the CO2-supply-closure event described in the prompt is not depicted at all.
level_2: At least one setup element appears (the aquarium, a seawater-like liquid, the colored dye, or a bottom-mounted diffuser), but none of them interact as described: bubbles are absent despite a diffuser being visible, the dye's color stays static with no bubbles ever introduced, or the CO2-supply closure is never shown or is shown in the wrong place.
level_3: A transparent aquarium containing liquid is visible; the liquid appears blue or purple, consistent with an unacidified pH indicator; a CO2 diffuser is visibly mounted at the aquarium's bottom; bubbles emerge continuously from it; the CO2 supply's closure is implied by the bubbles stopping; all the required elements are present, though the timing connecting the bubble stop to a visible closure cue may be unclear.
level_4: The scene meets the 3-point description, and in addition the aquarium is fully visible and filled uniformly with liquid, the pH indicator gives the liquid a stable initial blue/purple color, the CO2 diffuser stays fixed at the bottom and emits a continuous upward stream of bubbles, and the bubble stream begins, continues, and then stops cleanly and completely; the moment of stopping clearly and unambiguously marks the CO2 supply's closure, with no lingering trickle of bubbles afterward.
level_5: The scene meets the 4-point description, and in addition the aquarium walls show no distortion or reflection that hides its contents, the diffuser reads as built into the bottom surface rather than floating or suspended, the bubble stream stays continuous and vertically oriented and comes only from the diffuser, no further bubbles appear for the rest of the clip once the CO2 supply closes, and no extraneous object such as a hand, a tool, or an on-screen label enters the frame during the demonstration.

Scientific and Causal Correctness rubric:
level_1: The liquid shows no color change whatsoever throughout the clip; the bubbles are either absent or clearly not CO2, for example resembling ordinary air with no dissolving effect on color; the final color matches the initial color with no sign that acidification occurred.
level_2: The color changes, but in a way inconsistent with acidification: for instance the liquid goes straight from blue to yellow with no green stage, or from purple to red with no bubbles ever shown; or the color changes without any bubbles present; or bubbles appear but no color change ever follows.
level_3: The liquid starts blue or purple, a plausible neutral or alkaline pH; bubbles rise continuously from the bottom diffuser; the color gradually shifts to yellow or orange, a plausible acidic endpoint for indicators like bromothymol blue or phenol red; the shift begins only after the bubbles start and finishes stabilizing before the CO2 supply is closed; the direction and general correspondence to acidification are correct, though the timing may feel compressed or the color may not look perfectly even across the liquid.
level_4: The scene meets the 3-point description, and in addition: (a) the color shift looks uniform across the whole liquid body rather than in isolated patches or streaks; (b) the final stabilized color is clearly yellow or orange rather than green, brown, or pink; (c) the color, already stabilized before the bubbles stopped as required at the 3-point level, stays fixed afterward too, with no reversal or fluctuation once the CO2 supply closes; (d) no other visible tint, from lighting, on-screen text, or a reflection, masks or distorts the perceived hue.
level_5: The scene meets the 4-point description, and in addition: (a) the initial color reads unambiguously as blue rather than greenish or violet-tinged; (b) the shift passes visibly through green on its way to yellow/orange, with no stage skipped or reversed; (c) once stabilized, the final color shows no perceptible fading, brightening, or drifting for the remainder of the clip; (d) no rendering artifact, such as a color halo, glow, or washed-out over-saturation, affects how the hue reads anywhere in the liquid.

Spatiotemporal Consistency rubric:
level_1: The aquarium disappears and reappears; the liquid's level jumps to a different height; the bubbles jump between locations with no visible path connecting them; the diffuser changes position mid-clip; the lighting suddenly shifts, for example a flash, a strobe, or a brief blackout; or the camera appears to cut or pan.
level_2: It is a single continuous shot, but noticeable spatiotemporal breaks occur: the diffuser visibly shifts position between the bubbling and non-bubbling phases; the liquid surface goes from still to a sudden splash and back to still with no visible cause; the shadow cast by the diffuser or the bubbles vanishes or reappears without explanation; or the way light bends through the aquarium walls distorts object positions inconsistently from frame to frame.
level_3: The viewpoint stays fixed with no cuts, pans, or zooms; the aquarium stays fully in frame; the diffuser stays fixed at the bottom throughout; the bubbles rise continuously along consistent vertical paths; the liquid surface shows natural, low-amplitude movement that stays steady in character; shadows and highlights stay attached to their physical objects and do not jump around.
level_4: Motion meets the 3-point description, and in addition the bubbles' paths stay smooth and uninterrupted with no visible stutter, freeze, or dropped motion; the liquid surface's movement stays gentle and consistent rather than alternating between unnatural stillness and a sudden wave; the way light bends at the glass-water interface stays stable and physically plausible, for example no bubble appears doubled or inverted; and there is no visible mismatch in how foreground and background elements shift relative to each other over time.
level_5: Motion meets the 4-point description, and in addition the bubbles' sizes stay visually consistent with no abrupt shrinking or sudden merging; the liquid's transparency and the bubbles' visibility stay steady with no flicker between frames; the bubbles rise at a speed that looks natural rather than stroboscopic or jittery, and the diffuser shows no shimmering pattern; and all visible motion, such as bubble ascent and surface ripple, speeds up and slows down naturally rather than starting or stopping instantly like a mechanical toggle.