Domain: Healthcare — Clinical Laboratory Science
Target concept: Ascorbic Acid Determination (Neutral Red - Sodium Dichlorophenolindophenolate Method)

Video generation prompt: Collect 1 mL of urine from a patient with excess ascorbic acid, add 0.5 mL of neutral red - sodium 2,6-dichlorophenolindophenolate reagent, mix thoroughly, let stand for 1 minute, and observe the color change.

Evaluation guide:
(i) Target concept: Visual confirmation of ascorbic acid excess via specific chromogenic redox reaction.
Minimum mechanism: Ascorbic acid must be present in urine at sufficient concentration to fully reduce the dye reagent; neutral red must be co-present to form the pink/red complex; reduction requires time (1 min) for completion; color development must occur exclusively in liquid phase without interference from turbidity or pH shift.
(ii)Storyline: [Start] Clear tube containing ~1 mL pale-yellow urine → [Action 1] Dropper dispenses colored reagent (blue-green when concentrated, but diluted in urine it enables redox) into tube → [Action 2] Tube is mixed, inducing uniform dispersion → [State 1] Tube held motionless for full duration (no agitation) → [Phenomenon] Liquid transforms uniformly to pink/red → [Action 3] Observer directs gaze steadily at liquid column → [Visibility constraint] Entire sequence captured from fixed frontal angle; tube remains centered; lighting ensures color discriminability (no glare/masking); no occlusion of liquid column at any point.

Manual:
Experimental Procedure
1. Place 1 mL urine in a clear tube.
2. Add 0.5 mL neutral red–sodium 2,6-dichlorophenolindophenolate reagent.
3. Mix thoroughly by gentle inversion or stirring.
4. Let stand for 1 minute.
5. Observe color change.
Observation of Experimental Phenomena
Urine solution changes from colorless or pale yellow to pink or red after standing.
Summary of Experimental Principles
Ascorbic acid reduces oxidized sodium 2,6-dichlorophenolindophenolate (blue) to its leuco form, which complexes with neutral red to yield a stable pink/red chromogen.

Prompt Grounding rubric:
level_1: No urine sample container visible; no reagent bottle or dropper present; no mixing action shown; no 1-minute stillness period depicted; no color observation scene.
level_2: At least one correct object present (e.g., a clear liquid in a tube) but missing ≥2 of: urine container, reagent addition, mixing motion, stillness interval, or observation posture; sequence is scrambled (e.g., observation before addition).
level_3: Urine container (e.g., small transparent tube/vial) and reagent container (e.g., dropper or vial labeled/colored appropriately) both present; reagent is visibly dispensed into urine; mixing motion (stirring or vortexing) occurs; stillness follows mixing; observer looks at sample — all steps appear in correct sequential order with no missing core actions.
level_4: All elements from 3-score are present AND spatial relationships are preserved: reagent container and urine container remain side-by-side or adjacent throughout; mixing and stillness occur within same fixed viewpoint; observer’s gaze remains consistently directed at the sample during observation phase.
level_5: All elements from 4-score are present AND temporal sequencing is unbroken: reagent addition ends before mixing begins; mixing ends before stillness begins; stillness ends before observation begins; no cuts, jumps, or viewpoint shifts interrupt the causal chain; all objects retain consistent identity and labeling (e.g., no ambiguous unlabeled tubes substituting for urine or reagent).

Scientific and Causal Correctness rubric:
level_1: No color change occurs; sample remains colorless or unchanged throughout; reagent appears inert (e.g., colorless or same hue as urine); no contrast between pre- and post-reaction states.
level_2: A color appears but is incorrect (e.g., blue, green, purple, or yellow instead of pink/red); or color appears without reagent addition; or color change occurs before mixing or during mixing (not after stillness).
level_3: Color change from colorless/light-yellow (urine baseline) to pink or red appears after the stillness period; change is visually distinct and localized to the liquid phase; no other state changes (e.g., precipitation, bubbling, cloudiness) occur.
level_4: All elements from 3-score are present AND the color change is causally anchored: pink/red appears only after stillness (not during mixing or before addition); no competing phenomena (e.g., fading, streaking, gradient diffusion) obscure uniformity; color matches standard ascorbic acid-positive reaction (i.e., not orange, brown, or violet).
level_5: All elements from 4-score are present AND the pink/red color is stable, homogeneous, and confined solely to the liquid column; no discoloration at meniscus, no ring formation, no residue on container walls; color intensity is consistent across the visible depth of liquid; no visual artifact (e.g., glare, reflection, shadow) mimics or masks the true color state.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal rupture: objects teleport (e.g., tube appears in different position/orientation between shots); abrupt lighting shift (e.g., bright → dark mid-sequence); container deforms or fractures; liquid surface discontinuously jumps or vanishes.
level_2: Moderate inconsistency: mixing motion lacks continuity (e.g., jerky stop-start, unnatural acceleration); stillness period shows visible vibration or drift; observer’s head moves erratically during observation; container rotates or tilts without cause.
level_3: All motions are physically plausible: reagent dispensing shows controlled drop formation; mixing shows smooth rotational or back-and-forth motion; stillness shows zero observable movement of liquid surface or container; observation shows stable head/eye alignment with sample; no structural warping or lighting flicker.
level_4: All elements from 3-score are present AND spatial integrity is maintained: container maintains fixed position and orientation; liquid meniscus remains level and undisturbed during stillness; observer’s field-of-view remains centered on sample throughout observation; no parallax shift or zoom change breaks scene coherence.
level_5: All elements from 4-score are present AND temporal flow is seamless: frame-to-frame motion is smooth with no strobing, ghosting, or motion blur that obscures action; no inter-frame misalignment (e.g., liquid edge jitter, label jump); lighting remains uniform in tone and direction; no temporal compression/expansion (e.g., mixing appears unnaturally fast/slow relative to human-scale motor control).