Domain: Natural Science — Physics
Target concept: An ice cube with salt melts more quickly than a regular ice cube.

Video generation prompt: Place two identical ice cubes side by side on a dark tray; sprinkle coarse salt on the ice cube on the right, leaving the one on the left unchanged, and record with a fixed camera over an extended period until the ice cubes melt.

Evaluation guide:
(i) Target concept: Freezing point depression via solute addition (colligative property).
Minimum mechanism: Salt granules must stay in direct contact with the ice surface to locally depress the freezing point at that contact point below the surrounding temperature, triggering melt right where the salt sits; this local effect works whether the surrounding air is above or below 0°C, since it depends on salt-ice contact rather than a specific ambient temperature band; the ice must start free of any pre-existing surface contamination so the contrast between the two cubes stays visible.
(ii)Storyline: Frame 1–3: Two solid, identical, translucent-white ice cubes side-by-side on dark tray; coarse white salt granules clearly resting on right cube surface; left cube pristine and dry. Frame 4–7: Liquid water appears first and exclusively at salt–ice interface on right cube; water spreads gradually while preserving granule visibility; left cube shows no liquid, no surface depression, no edge rounding. Frame 8–10: Right cube exhibits expanding wet region with meniscus formation and possible granule partial submersion; left cube retains sharp edges and dry surface; spatial contrast in wetness/solidity remains unambiguous. Perspective: Fixed frontal view ensuring full visibility of both cubes' top surfaces and salt distribution; no occlusion, no parallax shift.

Manual:
Experimental Procedure
1. Place two identical, fully solid ice cubes side-by-side on a uniform dark, non-reflective tray.
2. Sprinkle dry, coarse, white salt granules only onto the right ice cube — leave left cube completely unsalted.
3. Record with a fixed, front-facing camera over an extended period, continuing until a clear difference in melting is visible between the two cubes.
Observation of Experimental Phenomena
The right (salted) ice cube develops visible liquid water earlier and more extensively at the salt contact zone, while the left (unsalted) cube remains predominantly solid with minimal surface wetness.
Summary of Experimental Principles
Salt lowers the freezing point of ice, causing localized melting at ambient temperature — an ice cube with salt melts more quickly than a regular ice cube.

Prompt Grounding rubric:
level_1: Two ice cubes are not both visible on the tray; or the tray is not a dark, opaque tray; or salt is nowhere in the frame; or only one ice cube appears; or the camera view is not fixed and front-on; or the two ice cubes are arranged in a stacked, diagonal, or overlapping pattern rather than side by side.
level_2: Both ice cubes and the dark tray are visible, but coarse salt is missing, is sprinkled on both cubes instead of only one, or is shown as a pre-dissolved brine rather than dry granules; or the two cubes are not arranged side by side; or the camera pans, zooms, or changes angle during the clip.
level_3: Two ice cubes of matching size sit side by side on a dark tray; coarse, dry salt granules are visible resting only on the right-hand cube; the left-hand cube has no salt on any surface; the camera holds one fixed, front-facing view of the whole tray; every object named in the prompt (two cubes, tray, salt) is present and positioned as described.
level_4: All conditions for score 3 are met, and the salt on the right cube is clearly loose and granular rather than clumped, wet, or dissolved at the first frame; both cubes are fully solid, with sharp edges and no melt, at video start; no hand, tool, or on-screen label ever enters the frame.
level_5: All conditions for score 4 are met, and the tray's dark surface is evenly lit with no glare or reflection that hides the ice or salt from view; individual salt grains are distinguishable from one another (not a single fused clump) on the right cube at the start; the left cube's surface is completely dry with no fog, condensation, or wetness at the first frame.

Scientific and Causal Correctness rubric:
level_1: Neither ice cube shows any melting; or both cubes melt at the same visible rate with no difference between them; or the salted (right) cube melts slower than or the same as the unsalted (left) cube; or liquid water appears only on the left cube; or the salt dissolves into the ice without any visible local melting around it.
level_2: One cube shows melting while the other stays completely solid and dry, but the melting is not tied to the salt's location — for example liquid appears on the left (unsalted) cube instead of the right; or the salt disappears from view without any visible melt forming underneath it.
level_3: The right (salted) cube develops visible liquid water at and around the salt grains earlier, or more extensively, than any wetness on the left (unsalted) cube; the left cube stays mostly solid with little or no surface liquid; the connection between the salt's location and the faster local melting is visually clear.
level_4: All conditions for score 3 are met, and the liquid on the right cube first appears exactly where the salt grains sit, not somewhere else on the cube; the left cube shows no pooling liquid or surface dimpling for as long as the contrast is visible; the salted cube is never seen melting later than, or at the same pace as, the unsalted cube.
level_5: All conditions for score 4 are met, and the wet region on the right cube keeps growing outward from the salt grains while the left cube stays visibly drier and more solid throughout; no frame shows the two cubes equally wet or equally rounded at the edges; the salt grains stay visible sitting in the forming meltwater until they are finally submerged.

Spatiotemporal Consistency rubric:
level_1: Either ice cube abruptly disappears or reappears between frames; the tray or background flickers out or is replaced; the room lighting jumps from bright to dark (or the reverse) within a single frame; an ice cube's size or shape changes in a sudden jump rather than gradually; the salt grains vanish or appear without any pouring motion; the camera view jumps to a new position or angle.
level_2: The camera drifts or wobbles slightly from its starting position; a hand or object enters the frame and then vanishes without a visible exit; the direction of the cubes' shadows changes partway through the clip; either cube becomes partly see-through or gets clipped at the frame edge; the tray's edge bends or warps in a way real trays cannot.
level_3: Neither cube disappears, reappears, or jumps position; the tray keeps its shape with no warping; both cubes' shadows point in the same direction and stay similarly dark across the clip; the camera does not move from its fixed, front-facing position; the two cubes stay in the same side-by-side arrangement relative to each other and the tray for the whole clip; any change in the cubes happens gradually, not in sudden jumps.
level_4: All conditions for score 3 are met, and the outline of each ice cube and the individual salt grains stay continuous from frame to frame with no flickering or shimmering along their edges; the tray's dark surface keeps a uniform, matte look with no sudden glare or flash breaking up the scene.
level_5: All conditions for score 4 are met, and the ice cubes' surface texture (frost patches, translucent patches) changes smoothly over time rather than in sudden jumps; the salt grains keep their individual shapes and stay scattered in a consistent pattern under the same lighting; neither cube nor the tray shows any bulging, bending, or curved distortion that isn't caused by the camera's fixed perspective.