Domain: Natural Science — Chemistry
Target concept: The solution color changes from yellow to red, forming a stable colloidal system.

Video generation prompt: Mix 1 mL of 1 mM HAuCl₄ aqueous solution with 1 mL of 10 mM sodium citrate aqueous solution, and heat to 100°C for 10 minutes.

Evaluation guide:
(i) Target concept: Citrate-mediated reduction of chloroauric acid yields stable, monodisperse gold nanoparticles exhibiting surface plasmon resonance absorption at ~520 nm, resulting in macroscopic red coloration and colloidal stability.
Minimum mechanism: Reduction must occur *after* mixing and *during* heating; citrate must be present in stoichiometric excess to prevent aggregation; absence of chloride contamination or rapid cooling prevents precipitation.
(ii)Storyline: Frame 1–2: Two static shots: left container holds pale yellow HAuCl₄ solution, right container holds colorless sodium citrate solution (side-by-side, same lighting, fixed viewpoint). Frame 3–4: Transfer action: liquid moves from one container to the other (or into third container), confirming contact and mixing. Frame 5–6: Heating initiates; visible thermal cues (steam, gentle bubbling, hotplate glow) appear *only after* mixing completes. Frame 7–10: Color transition progresses from yellow → orange → red; final state is uniformly hazy-red with no sediment, no interface separation, and persistent homogeneity. All events occur in fixed frame with no camera movement or cut.

Manual:
Experimental Procedure
1. Place 1 mL of pale yellow HAuCl₄ solution in a clean flask.
2. Place 1 mL of colorless sodium citrate solution in another clean flask.
3. Mix both solutions into a single flask.
4. Heat mixture to boiling for 10 minutes.
Observation of Experimental Phenomena
The solution changes from pale yellow to uniform, stable red; no precipitate forms; liquid remains homogeneous and colloidal (hazy-red, not transparent or grainy).
Summary of Experimental Principles
Gold nanoparticles nucleate and grow via citrate reduction of Au³⁺; citrate acts as both reducing agent and stabilizer, forming a stable red colloidal suspension.

Prompt Grounding rubric:
level_1: None of the required elements appear: no HAuCl₄ solution, no sodium citrate solution, no mixing action, no heat source, and no color change; the scene is unrelated to this synthesis.
level_2: At least one correct object appears (e.g., a beaker or a dropper), but the mixing action is missing or happens in the wrong order (e.g., heating starts before the two liquids ever combine); the two solutions are never shown separately before they meet.
level_3: The pale yellow HAuCl₄ solution and the colorless sodium citrate solution are shown separately before mixing; a mixing action (pouring or pipetting) is visible; a heat source (hotplate or boiling water bath) is present and active during or after mixing; all core elements (the two solutions, a container, and the heat source) are present and used in the right roles.
level_4: Everything from the 3-point level is present, and in addition the two liquids are shown being combined in comparable amounts (matching fill levels or a symmetrical pour, consistent with 1 mL + 1 mL), heating begins only once mixing is finished, and the container stays in the same spot in the frame throughout, with no extra objects or steps that don't belong in this procedure.
level_5: Everything from the 4-point level is present, and in addition the two liquids are shown side by side in the same shot before mixing, then combined into one container, followed by a clearly sustained heating cue (visible steam, bubbling, or a glowing hotplate), all captured in one continuous shot with a fixed camera and no cuts or repositioning.

Scientific and Causal Correctness rubric:
level_1: The solution never turns red (it stays yellow, or turns green, blue, purple, black, or clear instead), or the color change runs backward (red fading back toward yellow); no hazy, uniform colloidal appearance ever develops.
level_2: A color change happens, but not from yellow to red, e.g., yellow to orange, yellow to brown, or yellow to pink; or a red tint appears briefly and then fades; or red only shows up at the edges or as scattered specks rather than filling the whole liquid evenly.
level_3: The liquid turns from yellow to a uniform red during the clip, the red is even across the whole visible volume, the liquid stays smooth and single-phase (no visible flakes or settling), and the final state is a stable, hazy-to-translucent red suspension rather than a clear solution or a solid precipitate.
level_4: Everything from the 3-point level is present, and in addition the starting HAuCl₄ solution is clearly pale yellow before the two liquids combine, and the red color only appears once heating is underway; no red tint shows up before the heat source is visibly active.
level_5: Everything from the 4-point level is present, and in addition the red, hazy colloidal appearance holds steady all the way to the final frame (no fading, clouding, or darkening), with even color and haziness across the whole depth and surface of the liquid, and no streaks or a visible boundary layer anywhere in the container.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal breakdown: the container's shape or size changes, or it jumps to a different spot on the bench between frames; the liquid inside disappears and reappears; an unexplained abrupt lighting change occurs (e.g., a sudden switch from bright to dark); the shot cuts and restarts the scene from a different angle mid-heating; or the motion freezes or strobes for a large stretch of the clip (roughly a third or more of its total length).
level_2: Multiple moderate violations: the container appears to wobble or rotate on its own; the liquid surface jumps or sloshes with no pour, stir, or heat-driven convection to explain it; steam or bubbles appear and vanish between frames rather than building up continuously; or the glass's reflected highlight jumps to an inconsistent side without the camera or light source moving.
level_3: Minor but noticeable flaws: slight camera drift or a brief soft-focus moment; the liquid's meniscus line looks slightly different in shape between two nearby frames; one odd moment such as a bubble or droplet lingering in place too long; the container itself stays put and no liquid or color disappears outright.
level_4: Motion stays physically plausible throughout: the liquid pours and mixes smoothly, convection currents and rising steam build up gradually as heating proceeds, the container stays rigid and stays put on the bench, and the glass's highlight shifts only in ways consistent with the visible heat source and camera position; only a small flaw remains, such as one slightly abrupt puff of steam or a brief flicker in the hotplate's glow.
level_5: Full spatiotemporal integrity in one continuous, uncut shot: the container's shape, size, and position on the bench never change; the liquid's surface rises, ripples, or steams only as the visible heating and mixing would naturally cause; the glass's highlight and the container's cast shadow shift only together with the (unmoving) light source and camera, never independently of each other; and the color moves from pale yellow through orange to hazy red as one smooth, continuous gradient rather than in visible jumps.