Domain: Natural Science — Chemistry
Target concept: Red precipitate of diazo coupling reaction

Video generation prompt: Add 1 mL of 0.1 M diazonium salt solution to 2 mL of 0.1 M β-naphthol (2-naphthol) in NaOH solution, and allow to stand at room temperature for 5 minutes.

Evaluation guide:
(i) Target concept: Azo coupling reaction between diazonium ion and activated aromatic compound (β-naphthol) under basic conditions yields an insoluble red azo dye precipitate.
Minimum mechanism: Diazonium electrophile must contact deprotonated naphthoxide nucleophile in aqueous alkaline medium; coupling occurs rapidly at room temperature; product has low solubility and high molar absorptivity in red region → visible red solid.
(ii)Storyline: Frame 0–2: Two labeled/test-tube-identifiable containers stationary and adjacent. Frame 3–4: Continuous liquid transfer from donor to acceptor container. Frame 5: Transfer ends; both containers remain fixed. Frame 6–10: Stillness phase: red precipitate appears at bottom of acceptor tube, grows visibly, and remains motionless; supernatant stays optically clear; no external intervention or environmental change occurs. Perspective: Fixed frontal macro view capturing full height of acceptor tube; precipitate must be fully within field of view and unobscured.

Manual:
Experimental Procedure
1. Place two clear glass test tubes side-by-side: left tube contains colorless diazonium salt solution, right tube contains colorless β-naphthol in NaOH solution.
2. Transfer 1 mL of diazonium salt solution from left tube into right tube.
3. Let mixture stand undisturbed for 5 minutes.
Observation of Experimental Phenomena
A bright red precipitate forms and settles at the bottom of the right tube; the supernatant remains colorless and transparent.
Summary of Experimental Principles
Diazonium ions couple with β-naphthol under alkaline conditions to form an azo dye — 1-(phenylazo)-2-naphthol — which is insoluble and appears as a red precipitate.

Prompt Grounding rubric:
level_1: No test tube holding the colorless diazonium salt solution and no test tube holding the colorless β-naphthol/NaOH solution are shown; no liquid transfer between the two tubes is depicted; no standing period follows.
level_2: Only one of the two required tubes is present (the diazonium salt solution or the β-naphthol/NaOH solution), or the transfer is missing or misrepresented (e.g., poured from an unlabeled third vessel, or no visible pour at all), and no standing period is shown afterward.
level_3: Two test tubes appear side-by-side, one holding the colorless diazonium salt solution and the other holding the colorless β-naphthol in NaOH solution; the diazonium salt solution is poured into the naphthol/NaOH tube; the tubes then sit undisturbed for a standing period consistent with the 5-minute wait named in the prompt.
level_4: All of score 3, plus: the two tubes sit side-by-side before the transfer begins, the pour only goes from the diazonium tube into the naphthol/NaOH tube (never the reverse), and no extra containers, reagents, or labels contradicting these two named solutions appear anywhere in the shot.
level_5: All of score 4, plus: both tubes stay in the same side-by-side position for the whole clip with no repositioning or camera cut during the transfer or the standing period, the pour is one continuous, unbroken action, and the full height of the receiving tube stays inside the frame throughout the 5-minute stand.

Scientific and Causal Correctness rubric:
level_1: No red solid forms in the naphthol/NaOH tube during the standing period; instead the tube shows a blue, green, yellow, or black solid, gas bubbles, or no visible change at all; or a red solid is already present before the diazonium salt solution is added.
level_2: A reddish solid does appear, but the coupling chemistry is misrepresented: it dissolves back into the liquid shortly after forming, stays suspended as a haze instead of settling, forms on the tube wall rather than within the liquid, reads as pink/magenta/orange rather than red, or appears while the diazonium solution is still being poured in.
level_3: A red solid appears only once the pour has finished, forming and settling toward the bottom of the naphthol/NaOH tube during the standing period; the liquid above the solid stays clear and colorless with no cloudiness.
level_4: All of score 3, plus: the solid has a granular/flocculent look rather than needle-like crystals, its red color is even throughout with no patches of a different hue, and no side effects appear (no fading of the red, no extra liquid layers, no fogging of the tube).
level_5: All of score 4, plus: the red solid first becomes visible within the first half of the standing period and keeps building until the period ends, sitting motionless at the bottom the entire time with no swirling, floating chunks, or sudden sinking: the passive, gravity-driven settling expected of the 1-(phenylazo)-2-naphthol coupling product.

Spatiotemporal Consistency rubric:
level_1: The diazonium tube or the naphthol/NaOH tube vanishes and reappears somewhere else between frames, the scene lighting jumps abruptly (e.g., a bright bench cuts to darkness), frames are missing so the pour appears to start in mid-air with no beginning, or a tube visibly breaks apart and then appears whole again.
level_2: A tube rotates more than a quarter turn with no hand or support visibly causing it, the poured stream separates from either tube (a droplet hangs unconnected in mid-air), the red solid appears already fully formed in a single frame with no build-up shown, or the lab background changes to a different setting partway through the clip.
level_3: The tubes shift position slightly (less than a tenth of the frame's height) during the stand, the lighting flickers briefly for a moment, or motion blur briefly softens the liquid surface, but the red solid and its position at the tube bottom stay identifiable throughout.
level_4: All of score 3, plus: the lighting stays the same brightness and direction across the whole clip, the tube outlines stay crisp with no warping, the liquid surface in both tubes stays level and unbroken during the stand, and the red solid keeps the same position relative to the tube bottom in every frame.
level_5: All of score 4, plus: the pour and the standing period play out as one smooth, continuous motion with no visible skips or repeated moments, the camera viewpoint never zooms, pans, or tilts, no new glare or shadow appears that wasn't there before, and the red solid's grainy texture keeps changing gradually (grains clumping or settling) across several consecutive frames rather than jumping between states.