Domain: Natural Science — Marine Science
Target concept: Carbon dioxide is introduced into seawater, causing a color change in the pH indicator.

Video generation prompt: A transparent glass tank filled with seawater containing a dissolved liquid pH indicator, into which carbon dioxide is continuously introduced as bubbles through a submerged tube.

Evaluation guide:
(i) Target concept: Visual demonstration of CO₂-driven seawater acidification via pH indicator colorimetry.
Minimum mechanism: CO₂ must dissolve to form H₂CO₃; indicator must be chemically responsive to [H⁺] change; color transition must follow established chromatic order for that indicator; dissolution and reaction must occur in aqueous phase with observable spatial-temporal propagation.
(ii)Storyline: Frame 1–2: Static shot of filled glass tank with blue/purple seawater + indicator, tube inserted, no bubbles yet. Frame 3–4: First CO₂ bubbles emerge from tube tip and begin rising. Frame 5–7: Color change initiates locally around bubble trails and expands upward/downward; hue shifts sequentially (blue→green→yellow). Frame 8–10: Entire water column reaches final yellow hue; bubbles continue rising uninterrupted; no reversal or stagnation. Perspective: Fixed frontal view, full tank in frame, no occlusion, consistent scale and focus throughout.

Manual:
Experimental Procedure
1. Fill transparent glass tank with natural seawater.
2. Add liquid pH indicator (e.g., bromothymol blue) to seawater until uniformly colored (blue/purple).
3. Insert tube into tank and introduce CO₂ gas steadily to generate rising bubbles through the indicator-seawater mixture.
Observation of Experimental Phenomena
CO₂ bubbles rise continuously through the seawater; the water color changes progressively from blue/purple → green → yellow as acidity increases.
Summary of Experimental Principles
Dissolved CO₂ forms carbonic acid, lowering pH; pH indicator undergoes reversible protonation-dependent color change, visually demonstrating ocean acidification.

Prompt Grounding rubric:
level_1: No transparent glass tank is visible; seawater is absent; no tube introducing bubbles is shown; no liquid pH indicator is visible anywhere in the scene.
level_2: A transparent container appears but is not identifiable as a glass tank (e.g., a plastic beaker or a container of unclear material); the liquid is absent or reads as clear water or an arbitrary colored liquid rather than seawater; a tube is present but does not deliver bubbles; the pH indicator is absent or appears as a solid or powder rather than a liquid.
level_3: A transparent glass tank holding liquid is visible; the liquid reads as seawater (e.g., a faint blue-green tint or suspended particulates consistent with natural seawater); a tube enters the tank from above or the side; CO2 bubbles emerge from the tube tip into the liquid; a liquid pH indicator is present (as a distinct added layer or pre-mixed colorant), but its introduction timing or on-screen location does not line up with the bubble stream.
level_4: The transparent glass tank contains seawater; the tube is inserted into the tank and continuously emits CO2 bubbles into it; the liquid pH indicator is visibly present in the seawater (either pre-added or introduced alongside the bubbles) and stays evenly distributed rather than pooling or streaking; every object matches the posted prompt, with no extra tools, labels, hands, or on-screen overlays.
level_5: Everything required for score 4 holds, and in addition: the tube tip stays at the single insertion point established in the opening frames while continuously emitting bubbles for the full clip; the pH indicator remains fully dissolved in the seawater with no undissolved streak or separated layer; the tank, tube, seawater, and indicator match the posted prompt exactly for the entire clip, with no extra prop, label, or hand entering the frame at any point.

Scientific and Causal Correctness rubric:
level_1: The seawater's color never changes throughout the clip; the CO2 bubbles produce no visible effect on the liquid's hue; the pH indicator's color is missing entirely, is visibly the wrong hue for an alkaline seawater baseline (e.g., red instead of blue/purple), or stays static despite the continuous bubble stream.
level_2: A color change happens, but it runs the wrong direction for acidification (e.g., the seawater turns more blue/purple while bubbling, implying rising alkalinity) or shifts to a hue outside the normal pH-indicator sequence (e.g., an isolated orange or grey tint with no green stage); the color jumps to its final state as soon as the clip starts and then stays static; or the bubbles are absent while the color is changing.
level_3: The seawater and indicator start at a plausible baseline color (blue or purple, consistent with alkaline seawater); CO2 bubbles are visibly present; the color shifts toward yellow through an intermediate stage (e.g., blue to green to yellow) as expected for acidification; however the shift jumps between hues rather than blending smoothly, only changes near the bubble column rather than through the visible water body, or fails to progress evenly across the tank.
level_4: The baseline color is correct for the seawater-indicator mixture (blue/purple); CO2 bubbles are introduced continuously; the color shifts progressively (blue to green to yellow) and visibly spreads outward from the bubble column; the whole visible water volume reaches the final acidic color; no reversal, flicker, or hue that contradicts the expected sequence appears.
level_5: The baseline color is correct and even throughout the tank; CO2 bubbles rise continuously; the color change starts where the bubbles contact the water and spreads smoothly and evenly through the entire column, following the standard pH-indicator sequence (e.g., bromothymol blue: blue to green to yellow); the final color matches the expected acidic endpoint; no unmixed streak or floating patch of color appears, and the transition shows no pause, reversal, or skip.

Spatiotemporal Consistency rubric:
level_1: The seawater surface jumps or disappears between frames; CO2 bubbles jump from one depth to another with no visible path connecting the two positions; the feed tube disconnects from the tank in one frame and reappears reconnected in the next; the overall lighting suddenly switches (e.g., a shadow-free frame directly follows a strongly shadowed one); the tank edges visibly warp or shimmer.
level_2: CO2 bubbles pop in or out of existence between frames rather than rising continuously; the water surface's reflection pattern changes character from frame to frame with no smooth transition; the tube visibly wobbles or rotates with no apparent mechanical cause; the shadow the tube casts on the tank's back wall flips to the opposite side between consecutive frames; the tank or background shifts sideways or zooms with no camera-motion justification.
level_3: Bubbles rise with a consistent vertical orientation, though spacing between them may vary slightly or a bubble may pause briefly before continuing; the water surface keeps a stable, continuously visible meniscus; the tube stays in the same position and angle across the clip; lighting stays visibly steady with no sudden brightening, dimming, or shadow flip; no bubble, tube, or reflection flickers, duplicates, or breaks apart between frames.
level_4: Bubbles rise continuously along straight vertical paths at a visibly uniform spacing and size; the water surface stays still with steady, unmoving highlights; the tube holds a fixed pose with no visible repositioning; the overall lighting stays even and unchanging in both direction and brightness; the tube tip, the rising bubbles, and the dissolved indicator all remain visibly inside the tank at every frame.
level_5: Every bubble follows a smooth, unbroken rising path with no visible stutter, sudden size change, or skipped position; the water surface shows no visible ripple or vibration; the tube's position, angle, and insertion depth show no perceptible drift across the clip; lighting intensity and direction stay visibly constant; the tank and background show no visible parallax shift or edge warping; motion blur on the bubbles stays consistent with their visible rise speed and the camera's fixed position.