Domain: Natural Science — Environmental Science
Target concept: Rapid Determination of Soil Nitrogen Content (Colorimetric Method)

Video generation prompt: Take 2 mL of nitrogen-containing soil extract into a test tube, add 2 drops of Nessler's reagent, and shake thoroughly.

Evaluation guide:
(i) Target concept: Colorimetric detection of ammonium nitrogen via Nessler"s reagent requires aqueous ammonium ions, alkaline pH, and absence of interfering ions (e.g., Ca²⁺, Fe³⁺) to yield stable yellow complex. Minimum mechanism: Reagent must contact extract, mixing must occur, and reaction kinetics allow visible yellow development within seconds under ambient light.
(ii)Storyline: [Frame 0–1] Static shot: upright test tube containing ~2 mL pale liquid (soil extract) centered in frame. [Frame 2–3] Dropper enters top of frame, aligned vertically over tube opening; first drop detaches and falls. [Frame 4–5] Second drop detaches while first impacts liquid surface, visible splash ripple. [Frame 6–7] Hand grasps tube and initiates vigorous rotational shake; liquid swirls uniformly. [Frame 8–9] Yellow color emerges homogeneously across entire liquid volume, fully replacing original hue; no gradient, no sediment, no surface-only tint. Perspective: Fixed frontal view, eye-level, shallow depth of field keeping tube in focus; no occlusion of liquid column or droplet path.

Manual:
Experimental Procedure
1. Place a clean test tube on bench.
2. Using a dropper, add exactly 2 drops of Nessler"s reagent to 2 mL of soil extract already in the tube.
3. Cap tube and shake vigorously for 2 seconds.
Observation of Experimental Phenomena
A clear, uniform yellow color develops throughout the liquid after shaking; no precipitate forms.
Summary of Experimental Principles
Nessler"s reagent reacts with ammonium ions (NH₄⁺) in alkaline solution to form a yellow-brown colloidal iodide of mercury and ammonium (HgO·Hg(NH₂)I); intensity of yellow color correlates with nitrogen concentration.

Prompt Grounding rubric:
level_1: No test tube is visible; no pale soil-extract liquid is shown; no Nessler's reagent dropper or bottle appears; no hand or shaking action occurs; the scene shows nothing resembling a soil colorimetric nitrogen test.
level_2: A test tube, dropper, or liquid appears, but is not used correctly: e.g., the dropper is shown but releases no visible drops, the tube looks empty after reagent is claimed added, or the wrong glassware/tool appears (a pipette instead of a dropper, a beaker instead of a test tube).
level_3: A test tube holding pale soil-extract liquid is shown; a dropper holding Nessler's reagent is held above the tube; two distinct drops leave the dropper tip and land on the liquid surface; a shaking motion follows the second drop; the objects match the prompt (test tube, soil extract, Nessler's reagent dropper).
level_4: Everything in score 3 holds, and: the dropper reads as or visually matches Nessler's reagent packaging (amber glass body, rubber bulb, narrow tip); the test tube is a clear-walled, flat-bottomed cylinder; the liquid occupies roughly one-third to one-half of the tube's height, consistent with about 2 mL; the shaking is a clear rotational or side-to-side motion with visibly moving liquid.
level_5: Everything in score 4 holds, and: exactly two drops fall in quick succession with no third drop, matching each other in size and fall path; the test tube's position within the frame stays essentially fixed while it is held and shaken: the hand may lift and rotate it, but it is not carried out of frame or repositioned elsewhere in the shot; shaking follows directly from the second drop's impact with no idle pause; no extra object enters or leaves frame; nothing is substituted for the specified reagent or vessel (no water standing in for extract, no iodine standing in for Nessler's reagent).

Scientific and Causal Correctness rubric:
level_1: No color change occurs at all: the liquid stays the same pale straw color throughout; or the liquid turns a hue Nessler's reagent cannot produce (red, purple, or green); or color appears before the drops ever contact the liquid.
level_2: A color change happens but doesn't match the Nessler's reaction: e.g., a brown or black precipitate settles with no yellow tint anywhere in the liquid, the liquid darkens toward black immediately on contact, the yellow tint stays confined to a thin film at the very top and never mixes through the volume, or color appears at the drop-contact point before shaking begins.
level_3: After shaking, the liquid turns a uniform yellow throughout its full volume with no brown precipitate visible; the yellow appears only once shaking starts and persists afterward; before the drops were added, the liquid was pale or colorless.
level_4: Everything in score 3 holds, and: the yellow visibly deepens from pale to a fuller yellow while shaking continues; no cloudiness, haze, or floating particles appear at any point; the yellow stays even across the tube once shaking stops; the color doesn't fade or lighten again during the recorded time.
level_5: Everything in score 4 holds, and: the yellow becomes fully and evenly developed within about a second of shaking starting; there's no streaking, uneven patches, or localized dark spots during development; the color reaches the tube walls uniformly, with no isolated droplet of unmixed color left at the surface, confirming the shaking has fully blended the reagent through the extract.

Spatiotemporal Consistency rubric:
level_1: The test tube's position or size jumps abruptly between frames with no matching motion; the liquid appears to move from one container into a different one; the dropper vanishes and reappears; the lighting flickers strongly frame to frame; the background changes; or the shot cuts between visibly different clips without continuity.
level_2: The test tube rotates more than roughly 45° with no hand or support visible; a falling drop's path bends unnaturally (e.g., curves upward); the shaking starts before the second drop has finished falling; the liquid surface freezes mid-splash for several frames; or the video stutters, skipping or duplicating frames during the action.
level_3: A brief (one-to-two frame) occlusion of the drop hitting the liquid, slight handheld jitter during shaking, or a small shift in shadow under otherwise steady lighting is acceptable, so long as no object warps and the overall motion stays continuous and physically believable.
level_4: Everything in score 3 holds, and: the camera viewpoint stays fixed with no pan, tilt, or zoom; the test tube's base stays in the same general screen position frame to frame; each drop falls in a straight vertical line; the shaking accelerates and decelerates smoothly rather than jerkily; the liquid surface deforms continuously without tearing or clipping; the tube's rim and the liquid's meniscus stay aligned between frames.
level_5: Everything in score 4 holds, and: there's no visible motion-blur mismatch or shimmering along moving edges; the drop's impact produces a roughly symmetric ripple that spreads outward and settles naturally; the shaking produces a consistent, coherent wave motion in the liquid rather than random sloshing; the foreground liquid and background keep correct relative depth with no visible parallax error; the tube, liquid, and dropper keep their spatial relationships consistent for the whole sequence.