Domain: Natural Science — Chemistry
Target concept: Combustion of sulfur

Video generation prompt: Place a small amount of solid sulfur in a crucible and continue heating it in air.

Evaluation guide:
(i) Target concept: Gas-phase combustion of elemental sulfur requiring prior melting and vaporization to generate S₂ vapor for reaction with atmospheric oxygen.
Minimum mechanism: Sulfur must transition from solid → liquid → vapor (S₂) → exothermic oxidation → excited-state emission (blue/violet flame); absence of any intermediate state invalidates the causal chain.
(ii)Storyline: Frame 1–2: Static shot showing crucible with discrete yellow granules inside. Frame 3–4: Crucible base heats (visible flame contact or glow), sulfur begins softening. Frame 5–6: Clear phase change: granules coalesce into reflective orange-yellow liquid pool. Frame 7–9: Flame emerges *from liquid surface*, blue at base, pale violet at periphery, anchored continuously. Frame 10: Flame sustains only while heat applied; extinguishes rapidly when heat removed. Perspective: Fixed frontal view, crucible centered, full crucible and sulfur surface fully visible at all times; no occlusion; lighting reveals texture and phase state unambiguously.

Manual:
Experimental Procedure
1. Place a small amount of yellow solid sulfur into a ceramic/metal crucible.
2. Apply heat to the crucible base using a Bunsen burner until sulfur melts.
3. Continue heating until molten sulfur ignites, producing a blue flame with pale violet rim.
Observation of Experimental Phenomena
- Solid sulfur is bright yellow and granular.
- Upon heating, it melts into an orange-yellow mobile liquid.
- Ignition occurs after melting, yielding a steady blue flame with distinct pale violet outer edge.
- No solid residue remains after combustion.
Summary of Experimental Principles
Sulfur undergoes combustion in air: S(s) + O₂(g) → SO₂(g). The blue-violet flame results from excited sulfur dioxide and atomic sulfur emission bands. Melting must precede ignition because vaporization of S₂ molecules is required for gas-phase combustion.

Prompt Grounding rubric:
level_1: No crucible appears in the video, or solid sulfur is never shown, or no heat source (flame, burner, hot plate) is ever brought near the crucible; the basic setup described in the prompt (sulfur placed in a crucible and heated) is missing entirely.
level_2: A crucible is shown but is empty, or sulfur is shown outside the crucible (e.g., on a bench or in a beaker), or a heat source appears without ever contacting or being aimed at the crucible; the order 'sulfur placed in crucible, then heat applied' is reversed or cannot be determined.
level_3: A crucible visibly holding a small quantity of solid sulfur is heated by a burner flame or comparable heat source aimed at the crucible base, in the correct order, but the crucible's type is hard to identify (could be mistaken for a bowl or dish) or the sulfur's position inside it is only partly visible.
level_4: The crucible is clearly a lab crucible (shallow, heat-resistant, ceramic or metal) holding a visibly limited amount of solid sulfur; a heat source is aimed squarely at the crucible base for a sustained period; if a flame appears above the sulfur, it visibly originates from the crucible's contents rather than from an unrelated object; placement, heating, and any resulting flame occur in the prompt's order with no substituted equipment.
level_5: All 4-point conditions hold, and additionally: the crucible stays in the same position and fully in view for the whole clip; the sulfur is never replaced mid-shot by a different material; no unrelated tools, hands, or props enter the frame during heating; the heat source keeps contacting or aiming at the crucible continuously rather than being applied only in brief, disconnected taps.

Scientific and Causal Correctness rubric:
level_1: No combustion occurs anywhere in the clip: the sulfur stays a solid granular mass the whole time; or a different material burns instead of sulfur (e.g., paper or a wick); or the flame shown is a plain blue gas-burner flame unconnected to the sulfur; or the sulfur never visibly changes state at all.
level_2: The sulfur melts into a liquid but never ignites; or a flame appears above the crucible before any melting is shown; or the flame's color is inconsistent with sulfur combustion (e.g., orange, green, or bright white); or the molten sulfur turns to a dark/black residue while burning (real sulfur combustion leaves no solid residue; it converts to SO₂ gas); or a flame appears while no heat source is being applied.
level_3: Yellow solid sulfur is shown, then melts into a mobile orange-yellow liquid, and only after that does a flame with a blue base and a pale violet-tinged edge appear above the liquid surface; the flame fades once heating stops; however, at least one causal link is shaky: e.g., the flame appears only moments after melting rather than growing out of the molten surface, or it lingers noticeably after the heat is withdrawn.
level_4: The full sequence (yellow solid sulfur, melting into orange-yellow liquid, then a blue-based flame with a pale violet edge rising from the molten surface only once melting is well underway) appears in the correct order; flame size visibly tracks how much heat is being applied; no dark residue or soot is left in the crucible; the flame dies out within about a second of the heat source being pulled away.
level_5: All 4-point conditions hold, and additionally: the molten sulfur surface shows a subtle liquid sheen/shimmer rather than looking like a static painted color; the flame shows natural flicker and an upward drifting motion rather than sitting rigidly still; no smoke or soot is ever visible; the blue-to-violet color pattern of the flame stays consistent throughout the burn instead of drifting toward another hue or washing out; nothing about the depicted state changes, flame color, or absence of residue contradicts how sulfur actually burns in air.

Spatiotemporal Consistency rubric:
level_1: The crucible instantly appears in a different spot or at a different size between frames with no motion shown in between; the sulfur or the flame is simply missing in one frame and back in the next, with no visible cause shown; the whole scene's brightness or color cast changes abruptly from one frame to the next as if two different clips were spliced together; the crucible visibly buckles, cracks, or changes shape on its own.
level_2: The crucible rotates or shifts position for no physical reason (nothing touches it); the flame's base detaches from the sulfur and hovers or drifts to a spot clearly away from the liquid surface (more than roughly half the crucible's height above it); the visible amount of sulfur drops suddenly between frames rather than shrinking gradually as it burns; the crucible's cast shadow swings to a noticeably different angle even though nothing in the scene (flame, camera, external light) has moved to explain it.
level_3: The crucible stays in the same place in the frame; the sulfur (solid or molten) stays where it was placed inside the crucible; once a flame appears, it keeps rising continuously from the sulfur rather than blinking on and off; the overall brightness and the direction the shadows fall stay believably matched to the flame as the visible light source, without unexplained flickers; there is no visible cutting-away or reappearing of the crucible or its contents. Brief, ordinary camera softness during motion is acceptable.
level_4: The crucible shows no unexplained sliding or spinning across the whole clip; the sulfur's only motion is the slow pooling/flowing typical of melting, moving smoothly rather than in sudden jumps; the flame's base stays attached to the sulfur surface as the surface itself slowly changes, rather than detaching and re-anchoring elsewhere; the crucible's shadow direction and length change only as much as a moving/growing flame would plausibly cause, never abruptly reversing; nothing about the crucible or sulfur appears to warp, double, or momentarily vanish.
level_5: All 4-point conditions hold, and additionally: the flame's height grows and shrinks smoothly with the heating rather than snapping between sizes; the molten sulfur's surface shows a continuously shifting shimmer consistent with a real liquid rather than a static image of liquid; the crucible's outline stays coherent and undistorted in every frame; there is no visible looping, freezing, or repeated frame that breaks the sense of one continuous, physically plausible event from placement through heating.