Domain: Healthcare — Nutrition & Dietetics
Target concept: Under acidic conditions, the magnesium ion in chlorophyll is replaced by a hydrogen ion, forming pheophytin and resulting in a color change.

Video generation prompt: Take one test tube, add 10 mL of spinach juice, then add 1 mL of hydrochloric acid solution. Mix thoroughly by shaking, then place in a boiling water bath for 2 minutes. After cooling, observe the results.

Evaluation guide:
(i) Target concept: Acid-induced demetallation of chlorophyll yielding pheophytin with characteristic brown color shift.
Minimum mechanism: Chlorophyll must be present in aqueous extract; acid must contact and penetrate the pigment matrix; thermal energy must assist protonation kinetics; cooling must stabilize the resulting pheophytin without degradation.
(ii)Storyline: [Phase 1: Baseline] Green liquid in upright test tube, static, well-lit; establishes initial chlorophyll state. [Phase 2: Intervention] Acid droplets enter liquid, followed by vigorous shaking; confirms reagent delivery and mixing. [Phase 3: Activation] Tube immersed in boiling water bath with continuous steam emission; confirms thermal activation window. [Phase 4: Stabilization] Tube removed, placed on bench, steam ceases, liquid settles; confirms cooling and equilibration. [Phase 5: Outcome] Final still frame shows homogeneous olive-brown liquid; confirms pheophytin formation. All phases occur from fixed frontal macro viewpoint; no occlusion of test tube contents; meniscus and color fully visible in every phase.

Manual:
Experimental Procedure
1. Place test tube containing 10 mL green spinach juice on bench.
2. Add 1 mL hydrochloric acid solution into the tube.
3. Shake tube thoroughly to mix.
4. Place tube in boiling water bath for heating.
5. Remove tube, cool to room temperature, then observe.
Observation of Experimental Phenomena
Green spinach juice turns olive-brown after acid addition, boiling, and cooling.
Summary of Experimental Principles
Under acidic conditions, Mg²⁺ in chlorophyll is replaced by H⁺, forming pheophytin — a brown pigment.

Prompt Grounding rubric:
level_1: No test tube appears, or no spinach juice is shown in it, or hydrochloric acid is never added, or the boiling water bath scene never appears, or no cooling/observation step is shown, and no color outcome of any kind is depicted.
level_2: At least one of the required objects (the test tube or the spinach juice) is present, but none of the core actions occur: no acid is added, no mixing is shown, the tube is never placed in a boiling water bath, and there is no post-cooling observation moment.
level_3: A test tube containing green spinach juice is shown; hydrochloric acid is visibly added to it; a mixing action (shaking or swirling) follows; the tube is shown placed in a boiling water bath; a settled, still shot after the steam has stopped stands in for the cooling step before the final observation.
level_4: In addition to score 3, the acid container and the spinach juice are both visible in the same frame before the acid is added, the test tube is shown from the same fixed viewpoint throughout, the boiling water bath step clearly shows steam and the hot water surface with the tube immersed in it, and the cooling step appears as a distinct calm period after the steam has stopped and before the tube is examined.
level_5: In addition to score 4, all seven expected actions appear once each and in the correct order (tube with juice shown, acid poured in, immediate shaking, immediate transfer to the boiling water bath, a visible period of continued steaming, removal and placement on the bench, and a settled still period of at least one second before the final observation), with none of these steps skipped, reordered, or replaced by an unrelated action.

Scientific and Causal Correctness rubric:
level_1: No color change occurs anywhere in the sequence; the liquid stays uniformly green from start to finish; there is no visible link between adding the acid and any change in the liquid's color.
level_2: The liquid's color does change, but not correctly: for example it turns blue, purple, black, or fully colorless instead of brown, the color change happens before the acid is added, it occurs only during boiling without any acid ever being shown, or the green appears to deepen rather than fade.
level_3: The green spinach juice visibly turns olive-brown (or a similar brownish-green) after the acid has been added, the mixture has boiled, and it has cooled; the color change is confined to the liquid itself, without gas bubbles, precipitate, or other effects dominating the shot.
level_4: In addition to score 3, the color only shifts after the boiling-and-cooling sequence has completed (the liquid still looks green right after the acid is mixed in, before heating), and the final brown color is even and stable across the liquid, without vigorous bubbling, solid formation, or the liquid separating into layers.
level_5: In addition to score 4, the color change follows the expected sequence throughout: the liquid starts vivid green, stays green immediately after the acid is mixed in, fades gradually rather than instantly once boiling begins, and ends as a uniform olive-brown liquid after cooling, with no leftover green patches or uneven color gradient in the final result.

Spatiotemporal Consistency rubric:
level_1: The test tube or its liquid contents vanish from view and reappear in a later frame with no hand or visible cause moving them out of frame; the liquid's volume changes abruptly between shots with no pouring, shaking, or boiling shown; the scene jumps from bright, evenly lit to noticeably darker (or vice versa) within a single cut; or steam appears fully formed in a frame with no water bath or heat source visible beneath the tube.
level_2: One clear spatiotemporal flaw is present: the test tube appears rotated by a large angle between consecutive frames with no hand motion shown to explain it, the liquid's surface height jumps up or down with no visible pouring, shaking, or boiling causing it, or steam appears at full density in one frame with no gradual buildup from the water bath.
level_3: The test tube stays in the same position in the frame throughout; the liquid's level only changes during the acid addition, shaking, or boiling steps and not at other times; once boiling begins, steam rises gradually rather than appearing all at once; but one minor flaw is present, e.g., the tube's angle shifts very slightly between two consecutive frames without a corresponding hand movement, or the steam briefly thins and thickens unevenly.
level_4: All the continuity described in score 3 holds with no such flaw: the shaking motion looks like a natural back-and-forth oscillation rather than a rigid repeated snap, the steam during boiling rises in a smooth, ongoing stream rather than flickering on and off, and the transition from boiling to cooling shows the steam gradually tapering off rather than cutting off abruptly.
level_5: The entire sequence (from the initial green liquid, through acid addition, shaking, boiling, and cooling, to the final still shot) reads as one continuous, physically coherent process: the test tube's shape and the liquid's meniscus stay visually stable and plausible throughout, with no sudden shape changes and no liquid appearing to float above or sink below its surface, and the steam's rise and dissipation follow a single, uninterrupted, natural path with no abrupt cuts or flickering.