Domain: Natural Science — Chemistry
Target concept: Sodium metal reacts with chlorine gas

Video generation prompt: Place a small amount of solid sodium metal in a crucible, and heat the crucible to combustion inside a flask filled with chlorine gas.

Evaluation guide:
(i) Target concept: Exothermic redox synthesis of sodium chloride via direct combination of elemental sodium and chlorine gas.
Minimum mechanism: Sodium must be in solid metallic state pre-reaction; chlorine must be gaseous and present in stoichiometric excess; ignition requires thermal activation; product must be solid NaCl manifesting as white particulate smoke (not vapor or mist); no intermediate species or side products permitted.
(ii)Storyline: [Phase 1: Setup] Crucible centered in frame, empty; sodium placed into crucible (visible silvery-white solid, no oxidation); flask lowered over crucible or crucible inserted — greenish-yellow gas fully occupies flask volume with no air pockets. [Phase 2: Activation] Flame applied continuously to crucible base; no reaction until thermal threshold reached. [Phase 3: Reaction] Sudden onset of intense yellow flame localized around sodium; simultaneous emergence of dense white smoke from crucible rim; flame sustains <3 sec then self-extinguishes. [Phase 4: Outcome] White smoke remains suspended, gradually settling; crucible interior shows white powdery residue; no residual sodium or colored residues. Perspective: Fixed frontal view, full flask in frame, crucible fully visible, no occlusion; lighting consistent, no glare obscuring sodium or smoke.

Manual:
Experimental Procedure
1. Place a small piece of silvery-white solid sodium metal into a ceramic crucible.
2. Position the crucible inside a transparent flask pre-filled with chlorine gas (greenish-yellow).
3. Heat the bottom of the crucible with a flame until sodium ignites.
Observation of Experimental Phenomena
- Sodium burns with a bright yellow flame.
- Dense white smoke (sodium chloride solid) forms inside the flask.
- Flame extinguishes spontaneously; white smoke lingers.
Summary of Experimental Principles
Sodium metal reacts exothermically with chlorine gas to form sodium chloride: 2Na(s) + Cl₂(g) → 2NaCl(s). The reaction is highly vigorous, producing characteristic yellow flame and white crystalline smoke.

Prompt Grounding rubric:
level_1: No crucible is shown; no solid object representing sodium metal is placed in it; no flask or chamber containing chlorine gas is shown; no flame or heat source is applied to the crucible.
level_2: A crucible is present holding some solid, but the solid is not depicted as the described sodium sample (e.g., the wrong shape, or clearly a liquid); the flask shows no gas fill; heating is implied but the crucible is not shown inside or associated with the gas-filled flask; no reaction of any kind is attempted.
level_3: A small silvery-white solid (sodium) sits in a crucible that is inside a flask filled with greenish-yellow gas (chlorine); a flame is applied to the bottom of the crucible; a reaction is attempted, i.e., the sodium visibly ignites at some point after heating begins.
level_4: Everything in score 3 holds, and additionally the crucible stays in place inside the flask the whole time; the sodium is placed before the flame starts; the flame only touches the crucible after both the gas fill and the sodium placement are established; no flame appears outside the flask.
level_5: Everything in score 4 holds, and additionally the sodium sample looks lustrous and metallic before heating starts; the greenish-yellow gas visibly fills the whole flask with no obvious clear patches; the flame is aimed at the crucible base rather than its side or top; no stray objects, on-screen text, or overlays intrude on the shot.

Scientific and Causal Correctness rubric:
level_1: Combustion is shown without both sodium and chlorine gas present, or the flame is a color other than yellow (e.g., blue, red, or white), or the sodium looks liquid or dark before heating, or the gas is colorless, or no yellow flame or white smoke ever appears, or the end product looks like an unchanged metal or a liquid.
level_2: The sodium is solid but looks dull gray or black rather than silvery-white; or the gas looks colorless or only faintly tinted; or heating occurs with no ignition; or ignition happens with no heating shown beforehand; or the flame is orange, red, or white rather than yellow; or white smoke is missing or appears outside the flask.
level_3: The silvery-white sodium ignites in the chlorine-filled flask after heating, producing a bright yellow flame; dense white smoke (representing sodium chloride) appears inside the flask during or right after the flame; the flame dies out on its own after about two seconds and the white smoke lingers.
level_4: Everything in score 3 holds, and additionally the white smoke only appears after the flame starts, never before; the smoke is opaque and fairly uniform in whiteness rather than patchy or confined to one corner; the flame stays yellow throughout without an orange or red core or sudden color shifts; the sodium sample is fully consumed by the time the flame goes out, leaving no visible metal fragments.
level_5: Everything in score 4 holds, and additionally the flame only appears while both the sodium and the chlorine gas are present together, never from sodium or gas alone; a larger or smaller flame corresponds sensibly to the amount of sodium shown; the crucible's interior shows only a white powdery residue afterward, with no other-colored residue, sparks, or secondary flare-ups.

Spatiotemporal Consistency rubric:
level_1: The crucible or sodium sample appears suddenly inside the flask without ever being placed there; the flame appears with no visible heat source; smoke appears in the frame before any flame is visible; the gas inside the flask changes density abruptly partway through with no transition; or the lighting in the scene shifts abruptly between frames (e.g., a shadow vanishing and then reappearing) with no visible cause.
level_2: The crucible stays put but the sodium sample jumps into position rather than being placed continuously; the flame flickers on and off without any visible cause; smoke appears in separated puffs with visible gaps rather than a continuous plume; the crucible's apparent orientation or size changes between shots; or background objects behind the flask visibly warp or shear between frames.
level_3: The crucible stays in the same place and orientation throughout; the sodium is placed with continuous motion rather than a jump cut; the flame stays positioned at the crucible base the whole time it burns; the flame's start and end are gradual rather than an instant on/off; smoke rises continuously from the crucible area rather than in isolated bursts.
level_4: Everything in score 3 holds, and additionally the gas color inside the flask looks equally intense throughout the flask for the whole clip; the flame does not drift up, down, or sideways relative to the crucible while burning; the smoke plume flows upward without suddenly spreading sideways or stalling in place.
level_5: Everything in score 4 holds, and additionally the crucible does not visibly drift, resize, or reposition anywhere in the frame; the flame's origin stays visually anchored at the point where it contacts the crucible; the smoke's origin stays anchored at the crucible rim; motion of flame and smoke looks fluid rather than jittery or stepped, and no frames appear duplicated or dropped in a way that breaks the flow.