Domain: Natural Science — Earth Science
Target concept: Raoult's Law: Salt ions reduce the vapor pressure of water, resulting in a slower evaporation rate of saline water compared to pure water.

Video generation prompt: Two identical transparent evaporation pans were filled with equal volumes of distilled water and saline solution, respectively, and placed in the same ventilated and illuminated environment. The evaporation rates of the two were recorded by time-lapse photography, and the sequence of crystal formation at the bottom of the pans was observed.

Evaluation guide:
(i) Target concept: Dissolved salt lowers water's vapor pressure, so the saline pan evaporates more slowly than the distilled-water pan; because distilled water has no solute, it never reaches saturation and therefore never crystallizes, while the saline pan eventually crystallizes once its remaining liquid concentrates to saturation: a difference in *whether* crystallization happens, not evidence that slower evaporation itself speeds up crystallization.
Minimum mechanism: Liquid must remain stable (no boiling/turbulence); pans must be open to atmosphere; temperature and airflow identical for both; salt must be non-volatile and fully dissolved initially; crystallization requires supersaturation achieved via solvent loss, not cooling.
(ii)Storyline: Frame 0–2s: Both pans full, identical liquid height, no crystals. Frame 2–6s: Distilled pan liquid level drops steadily and noticeably faster; saline pan level drops slowly; no crystals yet. Frame 4–8s: First micro-crystals appear at bottom of saline pan while its liquid level remains measurably higher than distilled pan's current level. Frame 6–10s: Crystals grow visibly in saline pan; distilled pan liquid level reaches its lowest point (fully evaporated or nearly so) and remains crystal-free throughout, since pure water leaves no solute behind to precipitate. Entire sequence viewed from fixed frontal angle capturing both pans fully, with no occlusion, zoom, or repositioning.

Manual:
Experimental Procedure
1. Place two identical transparent evaporation pans side-by-side in fixed, well-lit, ventilated location.
2. Fill left pan with distilled water, right pan with saline solution (equal volumes).
3. Record time-lapse video capturing liquid level change and crystal formation at pan bottoms.
Observation of Experimental Phenomena
- Distilled water pan shows a faster decrease in liquid level and never develops crystals.
- Saline solution pan shows a slower decrease in liquid level; visible crystals eventually appear at its bottom once the remaining liquid concentrates to saturation.
Summary of Experimental Principles
- Raoult's Law: Dissolved salt ions reduce the vapor pressure of water, so the saline solution evaporates more slowly than distilled water. Crystallization timing depends on initial solute content, not on evaporation speed: the distilled-water pan contains no solute and therefore never reaches saturation or crystallizes however much of it evaporates, while the saline pan eventually crystallizes once continued (slower) evaporation concentrates it to its saturation point.

Prompt Grounding rubric:
level_1: The two pans, the distilled water, and the saline solution are not all shown together: e.g., only one pan is visible, the two pans are not placed next to each other in the same frame, or there is no sense of elapsed time (liquid levels and contents look identical in every frame).
level_2: Two pans are visible but are not clearly identical in size and shape, or only one liquid type appears to be present, or the pans sit apart rather than adjacent to each other, or the camera framing does not consistently keep both pans visible across the sequence.
level_3: Two identical transparent pans sit side by side in a single, steady shot; both contain liquid at the start; each pan keeps a consistent position throughout, but that position is never tied to which liquid is which: the only way to guess which pan started as distilled water and which as saline is to watch which one crystallizes later.
level_4: Everything at level 3 holds, and additionally: the pan positions (e.g., distilled on the left, saline on the right) are established in the very first frame, before either liquid level changes or any crystal forms, and the two pans never swap positions or get physically moved relative to each other afterward.
level_5: Everything at level 4 holds, and additionally: the pan identity (which is distilled, which is saline) is unambiguous from the opening frame alone, through a fixed, non-outcome-based cue such as a consistent position, a visible label, or a distinctly marked pan base, so a viewer could correctly say which pan is which even if the video were paused before any evaporation or crystallization had occurred.

Scientific and Causal Correctness rubric:
level_1: No evaporation-rate difference is visible between the two pans, or crystals appear first (or only) in the distilled-water pan, or the saline pan's liquid level drops as fast as or faster than the distilled pan's. There is no visible link between the presence of salt and either a slower liquid drop or a crystallization event.
level_2: Crystals appear in the distilled-water pan at any point, or crystals appear in the saline pan only after the distilled pan has already produced crystals, or the two pans' liquid levels fall at visibly the same rate with no crystal event in either.
level_3: The saline pan's liquid level visibly falls more slowly than the distilled pan's throughout; the distilled pan's level reaches its lowest point without ever producing crystals; crystals eventually appear at the bottom of the saline pan once its remaining liquid has concentrated substantially. This naturally happens only after most of the saline pan's liquid has evaporated, since a dilute solution needs that much concentration to reach saturation, and that delay is expected, not a flaw.
level_4: Everything at level 3 holds, and additionally: the saline pan's liquid level stays visibly higher than the distilled pan's at every matching timepoint, not just at the end, up until the distilled pan empties; the distilled pan never shows crystals at any frame; the saline crystals appear as discrete, faceted grains growing from the pan bottom rather than an amorphous film.
level_5: Everything at level 4 holds, and additionally: no frame shows crystals in the distilled pan before, during, or after the saline pan crystallizes; the saline pan's slower liquid drop and eventual crystallization stay consistent and unambiguous across the whole sequence with no tie, crossover, or reversal in which pan's level is higher; the distilled pan remains fully crystal-free through the entire recorded sequence.

Spatiotemporal Consistency rubric:
level_1: One or both pans vanish or appear abruptly between frames; a liquid surface jumps to a different height with no visible in-between draining; crystals appear instantly full-grown with no visible growth; a pan's outline warps or distorts between frames; the lighting flips or flashes with no connection to a normal lighting change.
level_2: A pan momentarily disappears and reappears; a liquid level rises back up or reverses direction partway through; an already-formed crystal cluster shifts position or orientation without staying attached to the pan bottom; the background or camera framing jumps erratically between frames.
level_3: Both pans stay visible in the same side-by-side arrangement for the whole sequence; each liquid level only ever goes down, never up, frame to frame; crystals grow gradually from the pan bottom rather than popping into existence; neither pan's shape warps; overall lighting stays reasonably steady aside from minor brightness unevenness or slight jitter in exactly where each pan sits.
level_4: Everything at level 3 holds, and additionally: both pans keep the same size, spacing, and position relative to each other throughout; each liquid level falls smoothly with no stair-stepping; crystal growth stays anchored to the pan bottom and expands continuously outward; lighting and shadow direction on the liquid surface change coherently rather than jumping between frames.
level_5: Everything at level 4 holds, and additionally: the pans' relative size, spacing, and orientation never drift for the entire sequence; each liquid surface recedes without stutter, pause-then-jump, or reversal; the saline pan's crystal growth begins from a single small nucleation point and expands outward without ever detaching or relocating; lighting, focus, and shadows change smoothly and consistently with a plausible steady light source throughout.