Domain: Healthcare — Nutrition and Food Hygiene
Target concept: Nitrite Detection

Video generation prompt: A 10-mL meat extract solution containing nitrite was placed in a test tube, followed by the addition of a solution of sulfanilic acid - Naphthylethylenediamine hydrochloride. The mixture was thoroughly shaken and allowed to stand.

Evaluation guide:
(i) Target concept: Visual confirmation of nitrite presence via diazo-coupling colorimetry.
Minimum mechanism: Acidic diazotization must precede coupling; color formation requires molecular collision facilitated by mixing (shaking), then stabilization via diffusion-controlled reaction during stillness; no color without both reagents and post-mixing rest.
(ii)Storyline: [Frame 0–2] Static shot: upright test tube with 10-mL pale-yellow liquid. [Frame 3–4] Reagent solution delivered from dropper into tube; clear liquid enters. [Frame 5–6] Hand grasps tube and performs ≥2 visible oscillatory shakes. [Frame 7–10] Tube released, held upright, fully motionless; pink hue emerges at ~frame 8, deepens to red by frame 10. All phases observed from fixed frontal angle; no occlusion; tube always fully in frame; lighting consistent; no secondary objects distracting from causal sequence.

Manual:
Experimental Procedure
1. A test tube contains 10 mL of pale-yellow meat extract solution.
2. A colorless sulfanilic acid–Naphthylethylenediamine hydrochloride solution is added dropwise.
3. The tube is shaken thoroughly by hand.
4. The tube is placed upright and left undisturbed.
Observation of Experimental Phenomena
A distinct pink-to-red color develops uniformly in the solution during the standing phase — no color change during addition or shaking alone.
Summary of Experimental Principles
Nitrite in meat extract undergoes diazotization with sulfanilic acid under acidic conditions, followed by coupling with Naphthylethylenediamine hydrochloride to form a stable azo dye — its red color intensity correlates with nitrite concentration.

Prompt Grounding rubric:
level_1: No test tube present; no meat extract solution visible; no sulfanilic acid–Naphthylethylenediamine hydrochloride solution shown; no shaking or standing action depicted; none of the three core objects (test tube, meat extract, reagent solution) appear.
level_2: Exactly one of the three core objects appears (e.g., only a test tube), but it is empty or contains unrelated liquid; no reagent addition, no shaking, no standing; no correspondence to posted_prompt sequence.
level_3: All three core objects are present: a test tube, a 10-mL meat extract solution (liquid, visibly in tube), and a separate reagent solution (labeled or visually distinct as sulfanilic acid–Naphthylethylenediamine hydrochloride); reagent is added to the tube; shaking action occurs; then stillness follows; all steps appear in correct sequential order with correct object types and quantities.
level_4: All conditions for score 3 are met, and additionally: the test tube is upright and stable throughout; the meat extract solution occupies approximately the lower half of the tube before addition; the reagent solution is delivered from a dropper or pipette into the tube (not poured from beaker); shaking is performed by hand-held tube with visible rotational/oscillatory motion; standing phase shows no further motion for ≥1 continuous visual interval.
level_5: All conditions for score 4 are met, and additionally: the reagent solution is delivered as discrete drops (≥3 visible drops entering tube during addition); shaking lasts for ≥2 full visible oscillations with consistent amplitude; the standing phase shows the tube completely still for at least 2 seconds of video time, with no visible movement of the tube at all; no object enters/exits frame mid-sequence; all actions occur within same fixed viewpoint without zoom or pan.

Scientific and Causal Correctness rubric:
level_1: No color change occurs; solution remains colorless or constant color throughout; any color shift contradicts nitrite detection (e.g., turns blue without pink/red intermediate); no causal link between addition/shaking and color development.
level_2: A single uniform color appears (e.g., solid blue or purple) immediately after addition: no pink/red hue at any point; or color appears before addition/shaking; or color develops only during shaking and vanishes during standing.
level_3: A pink-to-red color develops *after* shaking and *during* standing; the color is localized within the liquid phase (not on tube walls or air bubbles); the hue is objectively red-tinged (not yellow, green, blue, or brown); color appears only after shaking completes and persists through standing, satisfying the causal chain: addition → shaking → color development → stabilization.
level_4: All conditions for score 3 are met, and additionally: the color develops progressively: initial faint pink appears within first half of standing phase, intensifies to vivid red by end of standing; no competing hues (e.g., no simultaneous orange + purple patches); color is homogeneous across liquid volume (no streaking, layering, or cloudiness inconsistent with diazotization coupling).
level_5: All conditions for score 4 are met, and additionally: color development is exclusively confined to the aqueous phase; no color appears on tube interior above liquid meniscus; no precipitation, turbidity, or phase separation occurs at any time; intensity gradient (if any) follows natural diffusion pattern (darker at bottom, fading upward), matching real diazo-coupling kinetics; color matches a standard nitrite-positive reference (red, not magenta or scarlet).

Spatiotemporal Consistency rubric:
level_1: The test tube's position or the liquid's color jumps between frames with no visible transition: e.g., the tube appears in a new spot with no travel shown in between, the pale-yellow liquid turns straight to red with no pink stage, or the liquid vanishes or spurts out unexplained during shaking; the tube rotates more than a quarter turn with no hand visibly touching it; the scene abruptly flips between bright and dark lighting with no cause (no shake, no added light source); background objects pop in and out of view.
level_2: One clear continuity break occurs: the tube's position shifts noticeably between the reagent-addition step and the shaking step; the liquid's level or color changes with no visible cause between two consecutive frames; the shaking motion starts or stops with a visible skip; during the standing phase the liquid or tube still shows leftover swaying instead of settling into stillness.
level_3: The test tube stays centered and upright in the same spot throughout; the reagent stream visibly travels from the dropper down into the tube rather than appearing already mixed; the shaking motion swings smoothly back and forth without snapping or overshooting; once the hand releases the tube for the standing phase, the tube and liquid surface stop moving entirely: no rocking, no ripples.
level_4: All conditions for score 3 are met, AND the room's light source stays fixed, so the tube's glass highlight and the liquid's color read at the same brightness in every frame (no sudden glare or dimming); the background behind the tube stays unchanged; the liquid's meniscus keeps its curved shape throughout; the dropper tip stays visible and isn't unnaturally clipped at the frame edge while adding reagent.
level_5: All conditions for score 4 are met, AND the shaking motion looks smooth with no repeated or skipped frames; the liquid's surface catches light consistently as it moves during shaking, with no strobe-like flicker; the tube's glass thickness and curve look stable rather than warping between frames; the transitions from adding reagent, to shaking, to standing flow into each other with no hard cuts or freeze-frames.