Domain: Natural Science — Chemistry
Target concept: The precipitation rate becomes visible upon addition of an electrolyte (e.g.,

Video generation prompt: Two transparent beakers are placed side by side, the left one blue and the right one red, both containing sodium sulfate; the right beaker also contains sodium nitrate. A pipette simultaneously adds barium chloride to both.

Evaluation guide:
(i) Target concept: Electrolyte-accelerated visibility of barium sulfate precipitation.
Minimum mechanism: Ba2+ from the barium chloride reacts with the SO4^2- present in both beakers, so insoluble BaSO4 forms in both beakers; the right beaker's extra inert electrolyte (NaNO3) raises the solution's ionic strength, which compresses the electrical double layer around the newly formed colloidal BaSO4 particles and speeds up their coagulation into visible flocs; this makes the right beaker's precipitate turn visibly cloudy sooner and more densely than the left beaker's, even though both beakers eventually show precipitate.
(ii)Storyline: Frame 0–2: Two static, side-by-side beakers: left blue (Na2SO4 only), right red (Na2SO4 + NaNO3); both fully transparent and still. Frame 3–4: Pipette descends synchronously toward both beaker mouths; no liquid dispensed yet. Frame 5: First contact: barium chloride enters both solutions at the same moment. Frame 6–7: In the right beaker, white precipitate appears sharply and densely; the left beaker still looks clear or shows only a very faint haze. Frame 8–9: The right beaker's precipitate keeps intensifying (more particles, higher opacity); the left beaker now also begins showing sparse, delayed precipitate that stays visibly thinner than the right beaker's. Perspective: Fixed frontal view, centered on the beaker pair; no occlusion; full beaker height visible; pipette always in frame during the action.

Manual:
Experimental Procedure
1. Place two transparent beakers side-by-side.
2. Fill the left beaker with sodium sulfate solution and tint it blue; fill the right beaker with sodium sulfate plus sodium nitrate solution and tint it red.
3. Use a pipette to simultaneously add barium chloride solution to both beakers.
Observation of Experimental Phenomena
White precipitate forms in both beakers, but it appears earlier and more densely in the right (red) beaker; the left (blue) beaker shows delayed, sparser precipitate formation.
Summary of Experimental Principles
Barium chloride reacts with sulfate ions in both beakers to form insoluble barium sulfate. The extra sodium nitrate in the right beaker raises the solution's ionic strength, which speeds up coagulation of the initially colloidal barium sulfate particles into visible flocs — making the precipitate become visibly denser sooner in the right beaker, even though both beakers ultimately precipitate.

Prompt Grounding rubric:
level_1: Neither of the two required beakers is present, or only one beaker appears, or the two beakers are not shown side by side; no pipette action is shown; the left beaker is not blue and/or the right beaker is not red; nothing indicates sodium sulfate is present in either beaker; no addition of barium chloride is shown.
level_2: Two beakers appear side by side, but at least one setup detail is wrong: the left beaker is not blue, or the right beaker is not red; a pipette action is shown but does not reach both beakers at the same time; sodium sulfate is not visibly implied in one or both beakers; sodium nitrate is missing from the right beaker or mistakenly shown in the left beaker instead.
level_3: Two transparent beakers stand side by side; the left one is blue and the right one is red; both are visually or textually indicated to contain sodium sulfate; the right beaker additionally carries a label or cue, distinct from the left, indicating sodium nitrate; a pipette delivers liquid into both beakers at essentially the same moment.
level_4: Everything required for level 3 is shown, and in addition the pipette tip is clearly positioned above each beaker's mouth while dispensing; nothing blocks the view of either beaker's contents; any labels on the beakers (for example "Na2SO4" on both, "+ NaNO3" only on the right) stay legible and correctly placed; the pipette's motion toward both beakers looks synchronized, with both deliveries starting and finishing at essentially the same time.
level_5: Everything required for level 4 is shown, and in addition the pipette delivers a visually matching volume and drop trajectory to both beakers (the delivery paths and drop shapes look symmetric); both beaker colors stay stable and don't bleed or mix before the barium chloride is added; the camera position and the beakers' positions relative to each other never shift; every label stays fully visible and legible for the whole clip.

Scientific and Causal Correctness rubric:
level_1: Neither beaker shows any precipitate; or precipitate shows up identically in both beakers with no difference in timing or density; or precipitate appears before the barium chloride actually reaches the liquid; or a color change overshadows or replaces any precipitate; or precipitate appears only in the left beaker instead of being faster in the right.
level_2: Precipitate appears in only one beaker, and it is the left (blue) one, the wrong beaker for a faster response; or precipitate appears in both beakers but with no visible difference in how fast or how dense it forms; or the precipitate that does form is not white; or precipitate appears without ever showing the barium chloride reaching the liquid.
level_3: White precipitate appears in the right (red) beaker first and becomes visibly cloudy sooner after the barium chloride is added than anything happening in the left (blue) beaker; the left beaker eventually shows its own white precipitate too, just later and thinner, rather than staying perfectly clear forever; precipitate in both beakers only starts after the pipette actually delivers liquid; the precipitate looks granular and suspended rather than a color change or gas.
level_4: Everything required for level 3 is shown, and in addition the right beaker's precipitate is clearly denser and more opaque than the left beaker's at any matching point in time; the left beaker's eventual precipitate stays visibly sparser and thinner than the right's throughout the remaining clip, never catching up to match it; neither beaker shows a color fade or liquid-mixing effect unrelated to the precipitate; the precipitate in both beakers stays suspended rather than fully settling out during the clip.
level_5: Everything required for level 4 is shown, and in addition the right beaker's precipitate has a sharp, early onset immediately after the barium chloride contacts it, while the left beaker's onset is clearly delayed and stays visibly sparser for the rest of the clip; the timing gap between the two beakers' onset is unambiguous frame to frame; the precipitate's texture in both beakers stays fine-grained rather than clumping into large flakes; no bubbling, color shift, or layer separation appears in either beaker at any point.

Spatiotemporal Consistency rubric:
level_1: A beaker suddenly appears in a new spot with no motion connecting its old and new positions; the pipette vanishes and reappears somewhere else; the beaker colors flicker inconsistently frame to frame; the scene's brightness suddenly jumps between two very different looks; a beaker's edge visibly warps or bends mid-clip; a beaker's transparency suddenly flips (clear one moment, opaque the next) with nothing to explain it.
level_2: One serious continuity break occurs: for example the pipette disappears mid-motion and reappears somewhere else; a beaker's position shifts sideways or up/down between shots; precipitate appears all at once rather than growing visibly; the direction the light seems to come from flips partway through the clip; a reflection or shadow points in a direction that doesn't match where the light is coming from.
level_3: No beaker or pipette suddenly appears in a new place, no shape breaks apart, and no sudden brightness jump occurs; the pipette's motion toward the beakers reads as one continuous movement rather than a jump cut; the two beakers stay in the same positions relative to each other throughout; the right beaker's precipitate is shown building up gradually, starting faint then growing denser, rather than snapping into its final look instantly; every object's outline stays physically plausible throughout.
level_4: Everything required for level 3 is shown, and in addition the way objects appear to shift as the camera or hand moves stays consistent with a single fixed viewpoint, with nothing floating independently of the rest of the scene; any reflections on the beaker surfaces move naturally as if tied to that same viewpoint rather than staying frozen or jumping; the precipitate particles show some small natural drifting rather than looking perfectly rigid or frozen; the beaker rims and any labels line up consistently from one frame to the next.
level_5: Everything required for level 4 is shown, and in addition the whole clip is free of noticeable frame-to-frame wobble; the pipette tip keeps a steady, near-vertical path as it lowers into each beaker; the point where new precipitate first becomes visible in the right beaker stays at roughly the same height across frames rather than jumping around; any shadow cast by the pipette moves smoothly in step with the pipette itself; the liquid surfaces and precipitate never show flickering or strobing between frames.