Domain: Natural Science — Environmental Science
Target concept: Ammonia Nitrogen Determination in Water (Nessler's Reagent Colorimetric Method)

Video generation prompt: Take 2 mL of ammonia-nitrogen-containing clear water sample into a test tube, add 2 drops of Nessler's reagent, and shake vigorously.

Evaluation guide:
(i) Target concept: Visual confirmation of ammonia-nitrogen presence via instantaneous, homogeneous color development after reagent addition and mixing.
Minimum mechanism: Nessler's reagent must be chemically intact (not degraded), sample must contain NH4+ above detection threshold, and vigorous shaking must achieve colloidal dispersion; otherwise no amber-yellow color forms or it remains heterogeneous.
(ii)Storyline: [Frame 0–1] Static shot: upright test tube with 2 mL clear liquid visible inside; [Frame 2–3] Dropper enters frame from top, positions over tube mouth, releases first drop, fully formed, spherical, detaching cleanly; [Frame 4–5] Second identical drop released; [Frame 6] Drops contact liquid surface simultaneously; [Frame 7] Immediate onset of controlled rotational-vertical shake; [Frame 8] Liquid surface deforms uniformly; [Frame 9] Full amber-yellow color fills entire visible liquid volume with no gradients or omissions, all under fixed viewpoint, no cuts, no occlusion.

Manual:
Experimental Procedure
1. Place 2 mL of clear, colorless water sample into a clean, transparent cylindrical test tube.
2. Using a calibrated dropper, add exactly 2 drops of Nessler's reagent vertically into the sample.
3. Cap or hold test tube securely and shake vigorously for ~1 second.
Observation of Experimental Phenomena
A uniform amber-yellow color develops throughout the liquid immediately after shaking — no streaks, patches, or delayed appearance.
Summary of Experimental Principles
Nessler's reagent (K2HgI4 in strong alkali) reacts with NH4+ ions to form a colloidal iodide of mercury and ammonium, producing a yellow-to-brown color proportional to ammonia-nitrogen concentration. The color must be homogeneous and immediate upon mixing.

Prompt Grounding rubric:
level_1: No test tube present; no water sample visible; no Nessler's reagent bottle or dropper visible; no action of adding reagent; no shaking motion; none of the three core objects (test tube, water sample, Nessler's reagent) appear.
level_2: At least one core object appears (test tube, dropper, or liquid), but the sequence does not match the prompt: either no 2 mL sample is shown, or the reagent added is not 2 drops, or shaking never happens; the addition and shaking steps are missing or occur in reverse order.
level_3: All three core objects are present (test tube, clear water sample, Nessler's reagent dropper/bottle); the sample sits in the test tube; the reagent is added; shaking occurs, but at least one detail is off, e.g., the dropper releases more or fewer than 2 visible drops, the water sample looks turbid or colored beforehand, or the test tube's size looks implausible for a 2 mL sample.
level_4: All core objects are correctly shown: a transparent cylindrical test tube holding a small, clear, colorless liquid; Nessler's reagent delivered from a dropper as exactly two distinct drop formations; shaking applied to the test tube only after both drops have been added; no missing or extra step, no misidentified object.
level_5: All conditions for the 4-score level are met; additionally, both drops are fully formed and detach cleanly, entering the liquid without splashing or merging in mid-air; the test tube stays upright and still before the reagent is added; shaking begins right after the second drop lands; the dropper tip never touches the tube rim or dips into the liquid; the whole sequence plays out in one continuous shot from a fixed viewpoint.

Scientific and Causal Correctness rubric:
level_1: The liquid stays colorless the whole time; or it turns a color other than amber/yellow (e.g., blue, pink, green, brown); or a color appears before the reagent is added; or a color appears without any shaking having occurred.
level_2: A color change happens, but the hue is wrong (e.g., pale yellow with no amber tone, or orange/red), or it appears before the reagent is added, or it stays unchanged even after shaking, or it only shows on the surface without mixing through the liquid.
level_3: Amber-to-yellow color develops after shaking, but it is unevenly distributed: streaks, rings, or patches are visible, or the color intensity clearly differs between the top, middle, and bottom of the liquid, or the color takes more than about 2 seconds to appear after shaking starts.
level_4: A uniform amber-yellow color fills the entire liquid volume within about 1 second after shaking begins; the color looks the same across the whole visible cross-section of liquid; no colorless patches, surface-only tint, fading, or darkening remain by the end of the clip.
level_5: All conditions for the 4-score level are met; additionally, the frame right before full liquid contact after shaking shows no color, and the very next visible frame already shows the complete, uniform amber-yellow color with no partial, mottled, or translucent stage in between; the color stays stable through the rest of the video.

Spatiotemporal Consistency rubric:
level_1: The test tube vanishes from the shot for a moment and then reappears; the liquid level jumps up or down with no dropper action causing it; the dropper skips from one position to another with no path connecting them; the lighting flips abruptly between frames; the shaking motion shows impossible acceleration or a broken rotation; or unrelated scenes are spliced together.
level_2: The test tube wobbles unnaturally during shaking (sliding sideways or bouncing off a surface); the dropper moves inconsistently (jerky starts/stops, a non-straight path); the liquid surface forms a standing wave that never damps out, or shows an inverted meniscus; or background elements flicker or warp.
level_3: Slight jitter appears during shaking; brief motion blur momentarily obscures the drop count; the base of the test tube is briefly hidden during the shake; the camera angle shifts very slightly at one point; no full structural break occurs, but the liquid surface's shape is not perfectly consistent frame to frame.
level_4: All motion looks physically coherent: the dropper descends smoothly and vertically; drops detach cleanly and fall under gravity; the shake is a rotational-plus-vertical motion centered on the tube's axis; the liquid surface deforms continuously with no snapping or freezing; the liquid interior, drop entry point, and meniscus stay visible throughout.
level_5: All conditions for the 4-score level are met; additionally, no motion blur ever hides the drop count or the moment the color appears; the camera angle never shifts; the test tube keeps the same position, tilt, and apparent size in every frame; the liquid's motion during shaking is smooth, symmetric, and settles the same way each oscillation; no sudden lighting or shadow change occurs.