Domain: Natural Science — Chemistry
Target concept: Copper(II) sulfate crystals dissolve and diffuse in water.

Video generation prompt: Place copper sulfate crystals into a transparent glass beaker containing room-temperature still water, and observe the changes over time without disturbance.

Evaluation guide:
(i) Target concept: Dissolution-driven density-driven diffusion of Cu²⁺ ions in still water, initiating at solid-liquid interface.
Minimum mechanism: Solid crystals must contact water surface → local saturation → dissolution → higher-density Cu²⁺-rich solution sinks → vertical concentration gradient forms via combined diffusion and gentle convection.
(ii)Storyline: [Phase 1: Pre-contact] Crystals suspended above still water surface in fixed beaker; no motion except controlled placement. [Phase 2: Contact] Crystals touch water surface → transient meniscus deformation → no splash/ripple propagation beyond immediate zone. [Phase 3: Initiation] Blue color appears exclusively at interface, confined to crystal base. [Phase 4: Propagation] Blue region extends downward in continuous, vertically aligned plume; crystal size reduces monotonically. [Phase 5: Sustained] Plume remains coherent, no lateral dispersion, no re-emergence of crystals; view remains fixed side-on to show vertical alignment and spatial relationship. Visibility constraint: Entire beaker height must be visible; crystal-water interface and lower diffusion zone must be simultaneously in frame without cropping.

Manual:
Experimental Procedure
1. Place solid blue copper(II) sulfate crystals onto the surface of still, colorless water in a transparent glass beaker.
2. Observe without disturbance for 10 seconds.
Observation of Experimental Phenomena
- Crystals remain intact upon contact, then gradually diminish in size.
- Blue color appears at crystal-water interface and spreads downward as a continuous vertical gradient.
- Water remains transparent and still except for localized diffusion; no turbulence or mixing.
Summary of Experimental Principles
- Copper(II) sulfate pentahydrate (CuSO4·5H2O, the vivid blue hydrate form of the crystals used here) dissolves endothermically in water (ΔH°soln ≈ +11.7 kJ/mol): separating the Cu²⁺ and SO4²⁻ ions from the crystal lattice takes more energy than is released when those ions become hydrated, so the dissolution draws a small amount of heat from the surrounding water.
- Dissolved Cu²⁺ ions impart the characteristic blue color; because the resulting Cu²⁺-rich solution is denser than the surrounding water, it sinks and spreads downward via combined gravity-driven convection and molecular diffusion.

Prompt Grounding rubric:
level_1: No copper(II) sulfate crystals visible; no transparent glass beaker containing still water visible; no placement action shown; scene is unrelated (e.g., empty table, hand-only, wrong container, or moving liquid without crystals)
level_2: Copper(II) sulfate crystals are present AND a transparent glass beaker with liquid is present, but: crystals are not placed into the beaker OR beaker contains visibly turbulent/moving water OR crystals are placed outside the beaker OR multiple unrelated objects dominate frame
level_3: Crystals are placed into the beaker containing still water; both crystals and beaker are fully visible in same fixed viewpoint; water surface is level and undisturbed at time of placement; no other major prompt elements missing
level_4: All 3-point conditions met AND crystals remain fully above water surface during placement (no premature submersion before contact), AND beaker remains motionless throughout entire video, AND crystals are clearly distinguishable as solid blue crystals (not powder, not dissolved, not discolored), AND no extraneous hands/tools remain in frame after placement
level_5: All 4-point conditions met AND crystals make unambiguous first-contact with water surface at a single identifiable moment, AND the water surface is perfectly still immediately before contact, with only a brief, localized meniscus deformation at the point of contact that does not propagate into ripples beyond the immediate contact zone, AND crystals retain sharp cubic crystalline shape and vivid blue color immediately before and at first contact

Scientific and Causal Correctness rubric:
level_1: No diffusion observed; water remains uniformly colorless throughout; crystals show no dissolution or color change; or water turns uniform blue instantly without gradient; or crystals vanish abruptly without trace
level_2: Color change appears only in immediate vicinity of crystals but does not extend downward; OR color spreads upward or laterally instead of downward; OR crystals turn white/transparent while water stays colorless; OR blue region appears disconnected from crystal location
level_3: Blue color appears adjacent to crystals and extends downward from point of contact in continuous vertical gradient; crystals visibly diminish in size over time; water remains transparent (no cloudiness or precipitation); no mixing or stirring occurs
level_4: All 3-point conditions met AND blue region forms exclusively below crystals (not above or around sides), AND gradient is continuous (no abrupt color jumps or isolated blue blobs), AND crystal mass visibly reduces progressively (not all at once), AND no color appears in water before crystal contact
level_5: All 4-point conditions met AND blue region expands strictly downward in a smooth, continuous, vertically aligned plume originating solely from crystal-water interface; crystals maintain structural integrity until near-complete dissolution; no horizontal spread, no secondary plumes, no color saturation before full dissolution

Spatiotemporal Consistency rubric:
level_1: The glass beaker's position, size, or orientation abruptly changes from one frame to the next; the crystals jump to a new spot or vanish and reappear instead of dissolving in place; the water level rises or falls with no visible cause; the shadow cast by the beaker and the sinking crystals on the tabletop flips to a different direction or vanishes between frames with no corresponding change in the crystals' position to explain it; the beaker's outline visibly warps or breaks apart.
level_2: Smaller but still noticeable glitches: the beaker's edge visibly shifts or wobbles between frames even though nothing touched it, the crystals flicker or jitter as they fall toward the water, or the water surface shows a sudden burst of ripples and then freezes instead of settling naturally; or the image briefly goes out of focus and then sharpens again.
level_3: Beaker remains fixed in position, orientation, and scale; crystals move continuously from air into the water without teleportation or freeze; water surface remains stable (no visible ripples except transient impact disturbance); the shadow cast by the beaker and settling crystals on the tabletop stays fixed in direction and strength throughout.
level_4: All 3-point conditions are met, AND the crystals sink along a smooth, steady path with no zig-zag, pause, or sudden change in speed, AND any ripple caused by the crystals touching the water dies down naturally within about a second rather than lingering, AND no part of the beaker or crystals disappears behind another object unexpectedly.
level_5: All 4-point conditions are met, AND the beaker's straight sides stay parallel and undistorted in every frame, AND the crystals' outlines stay clearly defined as they move, without smearing or flickering, AND the water's curved meniscus and its reflections keep a consistent shape throughout, AND the video shows no repeated frames, stutters, or ghost trails.