Domain: Natural Science — Chemistry
Target concept: Ammonia gas and hydrogen chloride gas diffusing from both ends of a glass tube

Video generation prompt: A horizontal glass tube has cotton soaked in concentrated ammonia solution placed at the left end and cotton soaked in concentrated hydrochloric acid at the right end. The tube is sealed, allowing the vapors to diffuse toward each other.

Evaluation guide:
(i) Target concept: Diffusion-driven reaction front localization in a confined gaseous medium.
Minimum mechanism: Two volatile reactants must be introduced at fixed, separated positions; their gaseous species must travel through shared airspace; reaction must yield a visible solid product whose deposition location reflects relative diffusion rates (NH₃ > HCl → product nearer HCl end).
(ii)Storyline: [Phase 1] Static setup: sealed horizontal tube with distinct left (NH₃-cotton) and right (HCl-cotton) markers visible. [Phase 2] Gradual emergence: faint haze begins simultaneously near both cottons, thickening inward. [Phase 3] Convergence & nucleation: hazes meet and coalesce into a single opaque white ring at intermediate position, biased toward right end. [Phase 4] Stabilization: ring remains fixed, sharply defined, and does not spread, dissipate, or split. Perspective: fixed frontal orthographic view (no parallax, no rotation, no occlusion), ensuring unambiguous left/right spatial encoding and axial alignment.

Manual:
Experimental Procedure
1. Place cotton ball soaked in concentrated ammonia solution at left end of horizontal glass tube.
2. Place cotton ball soaked in concentrated hydrochloric acid solution at right end of same tube.
3. Seal tube ends.
Observation of Experimental Phenomena
A white ring of ammonium chloride solid forms between the two ends, closer to the hydrochloric acid end.
Summary of Experimental Principles
Ammonia gas (NH₃) and hydrogen chloride gas (HCl) diffuse through air in the tube; NH₃ diffuses faster due to lower molecular mass; they react to form solid NH₄Cl, precipitating where they meet — nearer the slower-diffusing HCl source.

Prompt Grounding rubric:
level_1: No horizontal glass tube visible; no cotton balls present; no left/right spatial labeling or visual distinction between ends; ammonia and hydrochloric acid sources not shown at opposite ends.
level_2: A horizontal glass tube is present, but cotton balls are absent or placed at same end; or only one reagent source (ammonia OR hydrochloric acid) is visible; or both cottons appear identical with no spatial differentiation (e.g., both centered, both on left, or no fixed viewpoint establishing left/right).
level_3: Horizontal glass tube visible; two cotton balls present; one cotton visibly located at left end, the other at right end; reagent labels or visual cues (e.g., text overlay, color-coding, or contextual props) indicate ammonia at left and hydrochloric acid at right, but no vapor diffusion motion or white ring formation shown.
level_4: Everything required for score 3 holds, and additionally: the tube is fully sealed at both ends immediately after the cotton balls are placed, with no gap or opening visible; the two cotton balls stay clearly distinguishable from each other (e.g., by position or labeling) so left/right identity is unambiguous; neither cotton ball is repositioned, removed, or topped up after its initial placement; the camera keeps the entire tube, both ends, and the space between them in frame.
level_5: Everything required for score 4 holds, and additionally: both cotton balls are placed and the tube is sealed before any visible change happens inside the tube; neither end is ever unsealed, disturbed, or refreshed with more liquid after sealing; there is no camera movement, cut, or occlusion at any point that would stop the viewer from continuously seeing both ends of the tube and the space between them.

Scientific and Causal Correctness rubric:
level_1: No white ring forms; or ring forms instantly at one end; or ring is colored (e.g., blue, yellow, pink); or ring appears before cotton placement; or both cottons produce identical vapor plumes without contrast.
level_2: White ring forms but at left end only, or right end only; or ring appears simultaneously at both ends; or ring forms *before* both cottons are fully positioned; or cottons show liquid dripping, melting, or smoke-like non-diffusive plumes instead of gradual vapor convergence.
level_3: White ring appears *once*, in a single continuous segment, located *between* the two cottons; cottons remain stationary and intact (no dissolution, no leakage); no color change in cottons; vapor movement is not depicted, but final ring position is intermediate, consistent with NH₃ and HCl diffusion rates (NH₃ faster, so ring closer to HCl end).
level_4: All elements of 3-score satisfied; additionally, the white ring is positioned *closer to the right end* (hydrochloric acid side), not equidistant, not closer to left; and no secondary rings, halos, or fragmented deposits appear.
level_5: All elements of 4-score satisfied; additionally, cottons show no discoloration, swelling, or wetness beyond initial saturation; no ring dissipation or fading during video; no condensation on tube walls unrelated to reaction; ring morphology is uniformly opaque white (not translucent, not grayish, not granular).

Spatiotemporal Consistency rubric:
level_1: The glass tube disappears and reappears, or one of the cotton balls jumps to a different spot without being moved there; the white ring flashes fully into view or vanishes in a single frame instead of forming gradually; the lighting suddenly switches (e.g., bright to dark) with no transition; the tube appears to bend, rotate, or the camera jumps without any camera movement shown.
level_2: The tube stays in place but visibly warps or its transparency flickers inconsistently; a cotton ball changes size or shape abruptly between frames; the white ring appears with a hard, cut-out edge instead of gradually thickening; shadows on the tube switch direction between frames for no reason.
level_3: The tube keeps the same shape and orientation throughout; both cotton balls stay fixed at their original left/right ends; the white ring, once it appears, stays in the same place and forms without a sudden flash-cut; the lighting and shadow direction stay the same throughout; nothing in the frame overlaps, clips through, or floats free of another object.
level_4: Everything required for score 3 holds, and additionally a faint haze is shown thickening gradually inward from each cotton ball rather than the ring appearing with no buildup; the haze near the ammonia end and the haze near the acid end are shown starting to appear at roughly the same time, not one well before the other.
level_5: Everything required for score 4 holds, and additionally there is no stutter or freeze-frame in the tube, cotton, or ring at any point; the cotton texture and the tube's glossiness look the same from start to finish; the ring's edge looks about as sharp as the rest of the scene rather than looking pasted on; nothing in the shot shifts sideways relative to anything else while the camera view stays fixed.