Domain: Healthcare — Nutrition and Food Hygiene
Target concept: Heavy Metal Selenium Detection

Video generation prompt: A test tube containing 10 mL of a food extract solution with excessive selenium ions was treated with the 2,3-diaminonaphthalene reagent, and the pH was adjusted to 1-2 with hydrochloric acid. The tube was then kept in the dark for 10 minutes, after which it was illuminated with a UV lamp.

Evaluation guide:
(i) Target concept: Confirmation of selenium presence through formation of the 4,5-benzopiazselenol complex from the reaction of Se(IV) with 2,3-diaminonaphthalene (DAN) under acidic, light-protected conditions, followed by observation of its UV-excited fluorescence.
Minimum mechanism: Acidic pH (1-2) must be established before the dark incubation step, which protects the forming piazselenol complex from photodecomposition; the complex does not glow on its own in a dark room: its yellow-green fluorescence only appears once the sample is illuminated with a UV excitation source such as a UV lamp; no fluorescence should appear under ordinary room light without UV illumination, and no other tested metal ion (e.g., Zn, Cu, Fe) produces this fluorescence under the same conditions.
(ii)Storyline: Frame 1–2: Static medium-close shot of an upright test tube holding 10 mL of clear liquid, no color. Frame 3–4: A dropper adds the 2,3-diaminonaphthalene reagent, with no visible color change. Frame 5–6: A separate dropper adds hydrochloric acid, with no visible color change. Frame 7: Room lighting dims to protect the sample during the dark incubation period; the tube sits undisturbed. Frame 8–9: A UV lamp is brought into frame and switched on, directing UV light at the tube. Frame 9–10: A yellow-green fluorescence becomes visible within the liquid only while the UV lamp illuminates it, confined to the solution and increasing in visible brightness, viewed from a fixed frontal perspective; the tube stays centered and fully visible with no occlusion; all actions occur within the same continuous camera view without cuts or zooms.

Manual:
Experimental Procedure
1. Place a test tube containing 10 mL of food extract solution.
2. Add 2,3-diaminonaphthalene reagent to the tube.
3. Add hydrochloric acid to adjust pH to 1–2.
4. Keep the tube in the dark for 10 minutes to protect the forming complex from photodecomposition.
5. Illuminate the tube with a UV lamp and observe (video ends with the tube under UV illumination).
Observation of Experimental Phenomena
No color change is visible before or during the dark incubation. Once illuminated with the UV lamp, a yellow-green fluorescence becomes visible within the solution, confined to the liquid volume, and is absent whenever the UV lamp is off.
Summary of Experimental Principles
Selenium(IV) ions react with 2,3-diaminonaphthalene under acidic conditions (pH 1–2) to form 4,5-benzopiazselenol, a fluorescent complex. The dark incubation protects the newly formed complex from photodecomposition; the complex's yellow-green fluorescence is only visible under UV excitation, not to the unaided eye in ordinary or dark conditions without a UV lamp.

Prompt Grounding rubric:
level_1: No test tube is shown; no food-extract liquid is visible; neither the 2,3-diaminonaphthalene reagent nor the hydrochloric acid is added; the room never dims and no UV lamp appears; none of the prompt's objects or steps are depicted.
level_2: A test tube appears, but no liquid is visible inside it, or neither reagent addition is shown, or the room lighting never changes and no UV lamp is ever brought into frame. The core procedural steps of reagent addition, acid addition, the dark period, and UV illumination are missing or cannot be identified in order.
level_3: A test tube holding liquid is shown; the 2,3-diaminonaphthalene reagent is visibly added; hydrochloric acid is visibly added; the room dims for a dark period, and a UV lamp appears and is aimed at the tube; all five elements (tube, reagent, acid, dark period, UV lamp) are present, but the order is wrong, for example the UV lamp appears before the dark period ends, or an element is spatially implausible, such as the UV lamp overlapping the tube's interior.
level_4: Everything described at the 3 level still holds, and in addition the steps occur in the correct order (reagent addition, then acid addition, then the dark period, then UV lamp illumination), with the reagent and acid bottles positioned near the tube rather than overlapping it, and the UV lamp positioned to plausibly illuminate the tube; one minor non-core flaw is acceptable, such as an unrelated piece of lab equipment visible in the background.
level_5: Every element (test tube, food-extract solution, 2,3-diaminonaphthalene reagent, hydrochloric acid, dark period, UV lamp) appears exactly once, correctly positioned, and in the correct order: the filled tube is shown first, then the reagent is added, then the acid is added, then the room dims, then the UV lamp is switched on and aimed at the tube; no extraneous objects appear, no object appears twice, and no object's position looks physically implausible relative to the others at any point.

Scientific and Causal Correctness rubric:
level_1: No fluorescence appears at any point, even once the UV lamp illuminates the tube; or a color other than yellow-green appears; or a visible glow appears in the dark before the UV lamp is switched on, which is not possible for this reaction.
level_2: A glow or color change appears, but not tied correctly to the UV lamp: for example it appears while the room is dark and the UV lamp is still off, or immediately upon reagent addition before the dark incubation period, or it fades away while the UV lamp remains on.
level_3: No visible color or glow appears until the UV lamp is switched on and aimed at the tube; once illuminated, a yellow-green glow becomes visible within the liquid; however, the glow appears with a delay after the UV lamp turns on, or briefly appears in the dark room before the lamp is actually lit.
level_4: The liquid shows no color under room light or during the dark period; as soon as the UV lamp illuminates the tube, a yellow-green fluorescence appears confined to the liquid, without also appearing on the tube's outer glass or exterior surface; turning the UV lamp away or off causes the glow to disappear or fade.
level_5: Everything described at the 4 level still holds, and in addition the yellow-green fluorescence appears promptly when the UV lamp illuminates the tube, stays confined to the liquid volume with no spillover glow onto the tube's exterior or the benchtop, and is visually distinct from any reflected UV-lamp light in the frame; the glow is absent at every moment the UV lamp is not shown illuminating the tube.

Spatiotemporal Consistency rubric:
level_1: The test tube is missing from a frame and turns up again later in a different spot; the 10 mL liquid volume changes abruptly with no pouring or removal shown; a reagent or acid droplet jumps directly from its bottle into the tube with no visible travel; the room lighting flickers erratically between bright and dark; the UV lamp appears already lit with no one switching it on.
level_2: The tube tips sharply and then snaps back upright with no support shown; the tilt of the liquid surface does not match the tube's orientation; a reagent stream enters the tube from a direction inconsistent with where its bottle is shown; the dark period lasts only a moment before the room relights on its own; the shadows in the room shift inconsistently between frames.
level_3: The tube shows slight jitter in position across frames; a hand briefly blocks the tube for a moment during an addition; the darkened room shows one frame that is noticeably brighter than its neighbors; the tube otherwise stays in the same place and shape throughout.
level_4: The test tube, reagent bottles, and UV lamp all stay in fixed, physically consistent positions relative to each other; the tube does not shift, rotate, or change size; the liquid surface rises smoothly and settles naturally as each reagent is added; the room dims in a single smooth transition rather than flickering; one minor non-core flaw is acceptable, such as a brief mismatch between the UV lamp's beam direction and the tube's visible highlight.
level_5: Everything described at the 4 level still holds, and in addition the tube's position and the liquid's height stay identical in every frame where they are visible; the reagent and acid droplets follow a smooth, continuous path from their bottles into the tube; the room's dimming and the UV lamp's turning on are each a single clean transition with no flicker, stutter, or reversal; the UV lamp's light falls consistently on the tube with no sudden jumps in beam direction or brightness.