Domain: Healthcare — Nutrition and Food Hygiene
Target concept: Determination of Heavy Metal Chromium

Video generation prompt: A test tube containing 10 mL of food processing solution with excessive chromium (VI) ions was treated with diphenylcarbazide reagent, and the pH was adjusted to 1-2 with sulfuric acid. The mixture was thoroughly shaken and allowed to stand.

Evaluation guide:
(i) Target concept: Visual confirmation of Cr(VI) presence via acid-catalyzed chromogenic reaction with diphenylcarbazide.
Minimum mechanism: Cr(VI) must be present in solution; diphenylcarbazide must be added; strong acid (H₂SO₄) must be added to achieve pH ≤2; oxidation must occur; complex formation must yield violet-red chromophore; shaking ensures homogeneity; standing allows color stabilization.
(ii)Storyline: [Frame 0–2] Test tube with clear liquid is shown; [Frame 3–4] Diphenylcarbazide reagent bottle approaches and dispenses into test tube (visible liquid transfer); [Frame 5–6] Sulfuric acid bottle approaches and dispenses into same test tube; [Frame 7–8] Hand grasps test tube and performs ≥3 rhythmic up-down shakes with visible liquid oscillation; [Frame 9] Hand places test tube upright on surface and withdraws completely; [Frame 10+] Test tube remains motionless, liquid surface settles, and violet-red color emerges uniformly across entire column within 1–2 seconds post-shake; no hand, tool, or environmental interference during standing phase. Fixed frontal mid-shot perspective maintained throughout; all events occur in strict linear sequence with no parallel or overlapping actions.

Manual:
Experimental Procedure
1. Pour diphenylcarbazide reagent into a test tube containing 10 mL food processing solution.
2. Add sulfuric acid to adjust pH to 1–2.
3. Shake test tube thoroughly.
4. Place test tube upright and let stand.
Observation of Experimental Phenomena
A distinct violet-red (magenta) color develops uniformly in the solution after shaking and standing.
Summary of Experimental Principles
Cr(VI) ions oxidize diphenylcarbazide to diphenylcarbazone in acidic medium (pH 1–2), forming a stable violet-red complex detectable by visual inspection.

Prompt Grounding rubric:
level_1: No test tube visible; no diphenylcarbazide reagent container shown; no sulfuric acid bottle present; no food processing solution visible; none of the three core objects (test tube, reagent, acid) appear in correct functional context.
level_2: At least one core object appears (e.g., test tube), but no reagent bottle or acid bottle is shown; or all three objects appear but are not spatially associated (e.g., reagent bottle off-screen while test tube is handled); or solution volume is unidentifiable and no 10 mL reference (e.g., calibrated markings) is visible.
level_3: Test tube containing liquid is present; diphenylcarbazide reagent bottle and sulfuric acid bottle both appear in frame; all three objects are co-located in same scene with fixed viewpoint; liquid is visibly inside test tube; no action sequence shown (e.g., no pouring, no shaking), but objects match posted_prompt description.
level_4: All three core objects present and co-located; test tube contains liquid; reagent is poured into the test tube (visible contact between the reagent bottle's tip and the tube opening); sulfuric acid is poured into the test tube (visible contact between the acid bottle's tip and the tube opening); shaking action occurs (test tube held and moved rhythmically); no missing step from the posted_prompt sequence; but the standing/stillness period after shaking is not clearly shown (e.g., the clip cuts away right after the last shake, or the tube is still being handled when the clip ends).
level_5: All three core objects present and co-located in fixed viewpoint; test tube contains liquid; reagent poured into test tube → acid poured into test tube → test tube shaken (continuous rhythmic motion) → test tube placed stationary on surface and remains motionless for observable duration (no movement, no hand interference); all actions occur in correct sequential order with clear causal adjacency (pouring precedes shaking, shaking precedes stillness); no extraneous objects, no occlusion, no temporal jump.

Scientific and Causal Correctness rubric:
level_1: The liquid stays clear and colorless for the entire clip with no color change ever appearing; or it turns a color that doesn't match the Cr(VI)-diphenylcarbazide reaction (e.g., blue, green, yellow, or purple instead of violet-red); or a color appears before the reagent or the acid has been added to the tube.
level_2: Color change occurs, but not exclusively after both reagent and acid addition, e.g., color appears during pouring or before acid addition; or color appears only transiently and vanishes before standing; or final color is inconsistent with Cr(VI)-diphenylcarbazide complex (i.e., not violet-red or magenta).
level_3: Violet-red (or magenta) color appears only after both reagent and acid are added and after shaking; color persists during standing phase; but color appears *during* shaking (not after) or appears without clear temporal separation from shaking action; or color develops unevenly (e.g., streaks, patches, cloudiness) suggesting incomplete mixing.
level_4: Violet-red (magenta) color appears *only after* shaking completes and test tube becomes still; color is uniform, homogeneous, and fully developed across entire liquid column; no fading, no gradient, no phase separation; all causal dependencies satisfied: reagent + acid + low pH + oxidation state + shaking → color; but color onset timing is ambiguous (e.g., no clear visual demarcation between last shake and first appearance of color).
level_5: Violet-red (magenta) color is absent during all pre-shaking phases; appears abruptly and uniformly within 1–2 seconds *after* shaking stops and test tube is fully stationary; color occupies entire liquid volume with full transparency consistency (no turbidity, no sediment, no meniscus distortion); color is stable and unchanging throughout standing period; no deviation from Cr(VI)-specific chromogenic reaction behavior.

Spatiotemporal Consistency rubric:
level_1: The test tube jumps from one position to another with no visible motion path connecting them; the liquid inside spills out or vanishes between one instant and the next with no visible cause; the scene switches from bright to dark (or the reverse) with no transition; the test tube appears to break apart or its bottom appears to detach; the shot cuts to a different framing partway through the action.
level_2: The test tube stays in frame but spins past 90 degrees in a single instant rather than turning smoothly; the liquid surface looks rigid and unmoving during shaking, or sloshes far more violently than the hand's motion would cause; the reagent or acid bottle tips and pours with no hand visibly holding or guiding it; the overall brightness of the shot jumps up or down abruptly with no visible cause.
level_3: The test tube's position shifts slightly but stays roughly centered in the shot; the hand enters and exits the frame in a consistent, believable way; the liquid surface rises, dips, and ripples plausibly while being shaken; there is no teleporting, no breaking apart, and no lighting cut; but there is some jerkiness in the hand or tube's motion, or the hand briefly blocks the view of the tube for a moment.
level_4: The test tube stays in the same spot without drifting sideways or spinning; the liquid's motion while being shaken is contained and smooth, settling naturally rather than sloshing on and on; the glass wall of the tube and the liquid inside stay clearly visible and undistorted; the shot stays bright enough throughout that the liquid's color is easy to judge at every stage; but one small flaw remains, such as the image briefly looking slightly soft or out of focus during the standing phase.
level_5: The test tube does not drift, rotate, or shift position at any point in the clip; the shaking motion slows down naturally to a smooth stop rather than cutting off abruptly; there is no motion blur that looks mismatched to how fast things are moving, and no sudden refocusing; the shot stays evenly lit throughout so that the liquid's true color is visible without glare, and the tube wall and liquid surface are never obscured.