Domain: Natural Science — Environmental Science
Target concept: Determination of Fluoride in Water by the Alizarin Zirconium Colorimetric Method

Video generation prompt: Add 2 mL of the fluorinated water sample to a test tube, and add 2 drops of alizarin zirconium indicator.

Evaluation guide:
(i) Target concept: Visual confirmation of fluoride presence via a bleaching (color-fading) reaction of a pre-colored zirconium-dye indicator.
Minimum mechanism: The alizarin zirconium indicator is itself pink-to-red before use; fluoride ions in the sample compete with the dye for zirconium, forming the more stable hexafluorozirconate complex and releasing free dye; this causes the mixture's color to fade toward a paler pink or yellow-pink, with the degree of fading increasing as fluoride concentration increases; the fading requires molecular contact and mixing, not mere proximity.
(ii)Storyline: [Frame 0] Static shot of empty vertical test tube. → [Action 1] 2 mL colorless fluorinated water sample poured steadily into the tube, filling to a stable meniscus; the liquid stays colorless and transparent. → [Pause] Liquid remains motionless. → [Action 2] Dropper carrying pink-red alizarin zirconium indicator descends; the first droplet falls and merges, producing a brief, localized pink-red tint where it lands. → [Action 3] The second droplet falls and merges; as both droplets disperse through the sample, the pink-red tint visibly pales toward a lighter pink or pale yellow-pink, spreading evenly through the liquid. → [Stabilization] The paled color persists uniformly; no further darkening, spreading, or secondary shift. Perspective: Fixed frontal close-up, full tube in frame, no obstructions, consistent lighting, shallow depth of field emphasizing the liquid column.

Manual:
Experimental Procedure
1. Place a clean, dry test tube vertically in a holder.
2. Add 2 mL of fluorinated water sample using a graduated cylinder or pipette.
3. Add exactly 2 drops of alizarin zirconium indicator solution using a calibrated dropper.
Observation of Experimental Phenomena
The pink-red indicator color visibly pales toward a lighter pink or pale yellow-pink as it mixes into the sample; the degree of fading increases with the fluoride concentration present.
Summary of Experimental Principles
The alizarin zirconium indicator is itself a pink-to-red zirconium-dye complex. Fluoride ions form an even more stable complex with zirconium (hexafluorozirconate), competitively displacing the dye and releasing it in its paler, uncomplexed form; this bleaches the mixture's color toward pale yellow-pink, with greater fluoride concentration producing more pronounced fading.

Prompt Grounding rubric:
level_1: No test tube is shown; no fluorinated water sample is visible; no alizarin zirconium indicator dropper or liquid appears; no liquid-adding action occurs; the scene bears no resemblance to a water fluoride test.
level_2: A test tube appears but is empty or holds the wrong liquid (e.g., an already deeply colored or opaque fluid); either the water sample or the indicator dropper is missing; no clear addition action takes place; or the liquid is added to the wrong vessel (a beaker, a flask, or a bare hand).
level_3: A clear, upright test tube holding a colorless, transparent liquid is shown; a dropper is held above the tube; two separate additions occur — first, roughly 2 mL of liquid filling the tube's bottom third to half, then two distinct droplets released from the same dropper; both go into the same tube; no other container or tool dominates the frame.
level_4: Everything in score 3 holds, and: the sample stays visibly colorless and at a steady volume until the droplets are added; the dropper is visually identifiable as the indicator source (a distinct pink-red or reddish liquid visible in its barrel, or a labeled/consistent bottle in the background); the two droplets fall one after another with visible separation (no mid-air merging); both land inside the tube without splashing over the rim or striking the tube wall.
level_5: Everything in score 4 holds, and: the tube is clean, upright, and centered in frame; the sample settles to a stable meniscus before the droplets are added; each droplet stays spherical and intact until it lands, entering the surface smoothly with no rebound; nothing obscures the droplet count or entry (no heavy motion blur, no reflection hiding the interface, no lens flare over the liquid).

Scientific and Causal Correctness rubric:
level_1: No color ever appears in the liquid (the pink-red indicator's own tint never shows or blends in); or the mixture ends up a deep, undiluted pink-red or magenta with no sign of fading; or an unrelated hue appears (blue, green, black); or color shows before either droplet has touched the sample.
level_2: A color appears but doesn't match the fading reaction: e.g., the pink-red intensifies rather than paling after mixing; the tint stays confined to the exact spot where a droplet landed and never spreads or fades through the liquid; the color shows up on the tube's outer wall or the dropper tip instead of inside the liquid; or the color appears before a droplet actually reaches the sample.
level_3: After both droplets merge into the sample, the initial pink-red tint visibly lightens toward a paler pink or pale yellow-pink, evenly through the liquid; the fading happens only once the droplets have contacted and mixed with the sample, and the paled color holds afterward; before either droplet was added, the sample was colorless.
level_4: Everything in score 3 holds, and: the fading reaches every part of the liquid column with no leftover streak or patch of the original deeper tint; no haze, precipitate, or bubbles accompany the fading; once the paler color is reached, it stays steady rather than continuing to drift.
level_5: Everything in score 4 holds, and: the fading visibly begins right as the second droplet fully merges and spreads outward through the liquid in a natural diffusion-like pattern; the settled hue reads as a believable pale pink or pink-yellow rather than a vivid, saturated red, magenta, or violet; the paled color shows no flicker, pulsing, or further darkening or lightening once it settles.

Spatiotemporal Consistency rubric:
level_1: The test tube's position, size, or presence changes abruptly between frames with no matching action; the liquid's volume jumps discontinuously; the dropper vanishes from one frame and reappears elsewhere; the lighting swings sharply between frames (bright to dark); the tube rotates more than about 30° with no visible cause; or the background geometry warps or breaks apart.
level_2: A falling droplet freezes or strobes for more than two consecutive frames; the liquid surface stays rigid with no meniscus response when a droplet lands; the tube shakes violently with no apparent cause; the shadow on the tube or bench swings to a new direction with no matching change in the scene; or the light source appears to move mid-sequence.
level_3: The test tube stays fixed in frame with a consistent orientation and position; the liquid's meniscus is stable before and after each addition; each droplet falls along a continuous, unbroken vertical path from dropper tip to liquid surface; no object blocks a key moment (like a hand covering the tube during an addition); the lighting on the tube and liquid changes only in ways consistent with the depicted motion.
level_4: Everything in score 3 holds, and: each droplet's descent shows a smooth, natural deceleration near impact rather than constant speed or a sudden jump; the liquid surface dimples and ripples naturally on contact and recovers without tearing or clipping; the tube's rim and the liquid's meniscus line up consistently between frames; the background stays static with no parallax mismatch.
level_5: Everything in score 4 holds, and: the tube walls show a plausible bending of whatever is visible behind the liquid; each droplet holds a roughly spherical shape until it lands, without stretching or shearing in mid-air; the meniscus settles back smoothly after each impact rather than staying disturbed; every frame follows naturally from the one before it, with no jump cuts, repeated frames, or motion running backward.