Domain: Natural Science — Chemistry
Target concept: Nitration of benzene

Video generation prompt: Add a mixture of benzene, concentrated nitric acid, and concentrated sulfuric acid to a test tube, and heat it in a water bath to 55 ℃. After the reaction is complete, observe the liquid in the test tube.

Evaluation guide:
(i) Target concept: Formation of nitrobenzene via electrophilic aromatic substitution under controlled nitrating conditions.
Minimum mechanism: Benzene must remain intact (no oxidation), nitronium ion must be generated *in situ*, reaction must proceed without vigorous exotherm or decomposition, and product must separate as immiscible organic phase due to polarity difference.
(ii)Storyline: [Frame 0–2] Test tube on bench with clear benzene layer visible; [Frame 3–4] Conc. HNO₃ and conc. H₂SO₄ poured together into tube → immediate formation of heterogeneous mixture (slight fuming may occur but not required); [Frame 5–6] Tube placed upright into visible water bath; [Frame 7–8] Static dwell in bath (no boiling, no splashing); [Frame 9–10] Final frame shows two stable, sharply separated layers in same tube: upper yellow oil, lower colorless liquid. All events occur from fixed frontal viewpoint; no camera movement; no cutaways; layers must be visible without annotation or zoom.

Manual:
Experimental Procedure
1. Add benzene, concentrated nitric acid, and concentrated sulfuric acid into a test tube.
2. Place test tube in water bath heated to 55 ℃ for reaction.
3. After reaction, observe liquid in test tube.
Observation of Experimental Phenomena
A yellow oil layer (nitrobenzene) forms and floats on top of a colorless aqueous layer.
Summary of Experimental Principles
Electrophilic aromatic substitution: benzene reacts with nitronium ion (NO₂⁺) generated from HNO₃/H₂SO₄ to form nitrobenzene.

Prompt Grounding rubric:
level_1: No test tube present; no benzene, concentrated nitric acid, or concentrated sulfuric acid visible; no water bath setup; no heating action shown; no liquid observed in container at end.
level_2: Test tube present but empty or containing only one reagent; water bath or heating action absent or misidentified (e.g., flame instead of water bath); no mixture visibly added; final liquid not shown or shown in wrong container.
level_3: Test tube present and contains a clear liquid at start; three reagents (benzene, conc. HNO₃, conc. H₂SO₄) are all visibly added to the test tube in sequence (or simultaneously as a pre-mixed pour); water bath is present and test tube is placed inside it; final liquid is observed in the same test tube after heating.
level_4: All elements from score 3 present AND reagents are added before placement in water bath (correct temporal order); test tube remains in water bath throughout heating phase; final liquid remains in same test tube with no transfer, spillage, or replacement; no extraneous objects (e.g., stir bar, thermometer) introduced without justification.
level_5: All elements from score 4 present AND reagents are added in correct physical forms: benzene as colorless liquid layer, conc. HNO₃ and conc. H₂SO₄ as co-poured viscous amber/yellowish mixture (visually distinct from benzene); water bath shows visible water surface and stable immersion level; final liquid shows distinct yellow oil layer (nitrobenzene) separating from aqueous layer — both layers remain in same test tube, unmixed, with clear interface.

Scientific and Causal Correctness rubric:
level_1: No chemical change observable; liquid remains colorless and homogeneous throughout; no layer separation; no color change; no evidence of reaction product formation.
level_2: Liquid changes color but uniformly (e.g., entire solution turns yellow); no phase separation; or separation occurs without correct layer identity (e.g., top layer colored but bottom layer missing or inverted); or color appears before heating begins.
level_3: Final liquid shows two immiscible layers: upper layer is pale yellow to yellow, lower layer is colorless or faintly yellow; upper layer is less dense and floats; color appears only after heating phase completes; no bubbling, fuming, or violent reaction depicted.
level_4: All elements from score 3 present AND upper layer is distinctly yellow (not orange/red/brown); lower layer is transparent and colorless (not cloudy, turbid, or brownish); interface between layers is sharp and horizontal; no dissolution or emulsification observed; no gas evolution, charring, or decomposition signs.
level_5: All elements from score 4 present AND upper yellow layer has oily sheen and meniscus curvature consistent with organic liquid; lower layer shows meniscus consistent with aqueous density; no interfacial mixing or droplet suspension; color intensity and layer thickness ratio remain stable for ≥2 seconds post-heating without drift or coalescence.

Spatiotemporal Consistency rubric:
level_1: Test tube teleports between shots; water bath disappears/reappears; liquid level jumps discontinuously; lighting changes abruptly (e.g., bright → dark mid-sequence); container rotates or flips unnaturally; background shifts violently.
level_2: Test tube remains in frame but changes size/position inconsistently across cuts; water bath visible only in some frames then gone; liquid surface flickers erratically; shadow direction reverses; container edge warps or bends unnaturally.
level_3: Test tube stays fixed in frame with consistent position, orientation, and scale; water bath remains continuously visible beneath test tube; liquid surface remains level and stable during static phases; lighting and shadows remain directionally consistent; no object clipping or occlusion inconsistency.
level_4: All elements from score 3 present AND motion is smooth and physically plausible: pouring action shows continuous liquid flow without stutter or freeze; immersion into water bath shows unbroken descent path; no frame duplication or ghosting; no abrupt focus shift that hides layer formation.
level_5: All elements from score 4 present AND spatial relationships are preserved across all frames: test tube always centered above water bath; upper and lower layers maintain fixed vertical alignment relative to tube walls; no parallax shift between layers and container edges; no inter-frame jitter, warping, or perspective distortion.