Domain: Natural Science — Chemistry
Target concept: Reaction between magnesium and hydrochloric acid

Video generation prompt: A test tube contains colorless dilute hydrochloric acid, into which a silvery magnesium strip is placed.

Evaluation guide:
(i) Target concept: Gas evolution via single-displacement redox reaction between active metal and strong acid.
Minimum mechanism: Magnesium must be in direct physical contact with aqueous H⁺ ions; hydrogen gas nucleation requires heterogeneous surface; dissolution must proceed stoichiometrically without side products (e.g., no MgO formation, no Cl₂).
(ii)Storyline: [Phase 1: Pre-contact] Static shot: upright test tube with flat, still, colorless liquid surface and visible meniscus; silvery strip held above tube, fully illuminated, no bubbles. [Phase 2: Contact] Strip tip touches liquid surface → immediate bubble nucleation *at point of contact*. [Phase 3: Reaction] Bubbles ascend *only* from submerged strip surface; strip length decreases monotonically; no liquid turbidity or color shift. [Phase 4: Continuity] All elements maintain fixed spatial relationship (tube center-frame, strip vertical, bubbles rising straight); lighting/shadow stable; no cut or perspective shift. Visibility constraint: Entire strip length and full tube height must remain fully in-frame at all times; no occlusion by hand or equipment after initial placement.

Manual:
Experimental Procedure
1. Hold a clean, transparent cylindrical test tube containing colorless dilute hydrochloric acid.
2. Place a straight, silvery magnesium strip vertically into the acid so it is fully submerged.
Observation of Experimental Phenomena
- Immediate formation of colorless, spherical bubbles rising continuously from the strip surface.
- Gradual shortening and thinning of the magnesium strip during bubbling.
- No color change, precipitate, or smoke; liquid remains colorless and transparent.
Summary of Experimental Principles
Magnesium metal reacts with dilute hydrochloric acid to produce magnesium chloride (soluble) and hydrogen gas: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g). The bubbles are hydrogen gas; the strip dissolves due to oxidation of Mg⁰ to Mg²⁺.

Prompt Grounding rubric:
level_1: No test tube, no colorless hydrochloric acid, and no silvery magnesium strip appear together; one or more of these is missing, or the scene shows something unrelated (an empty bench, a different container, or no strip at all).
level_2: A test tube, colorless liquid, or metal strip appears, but not all three together; the strip is never brought toward or lowered into the tube; or an object clashes with the setup (e.g., the liquid is tinted, the tube is opaque, or the strip is black/oxidized rather than silvery).
level_3: A transparent test tube holding colorless liquid is shown, and a silvery magnesium strip is lowered until it touches the liquid surface; the contact between strip and liquid is unambiguous; no object's color, shape, or count contradicts the prompt.
level_4: Everything needed for a 3 is present, plus: the strip stays bright silvery and the liquid stays clear and colorless right up until contact; the tube is upright and cylindrical with clearly visible walls; the strip is lowered in one uninterrupted motion rather than being swapped or repositioned partway through.
level_5: Everything needed for a 4 is present, plus: the strip enters straight down the center of the tube rather than at an angle; the strip is shown as one intact, unbent, unbroken ribbon; the liquid surface is calm and flat in the instant before contact; the camera holds a single fixed, front-on framing that keeps the full tube and the entire strip length in view throughout.

Scientific and Causal Correctness rubric:
level_1: No reaction is visible at the droplet-contact point: the gray Zn/I2 blend stays unchanged, with no darkening, no vapor, and no haze; the water droplet simply beads up, evaporates, or vanishes without any visible effect.
level_2: Some reaction-like effect appears but breaks the basic cause-and-effect of the Mg + HCl reaction: bubbles form before the strip touches the acid, the strip shrinks with no bubbles at all, the acid turns yellow/green or cloudy with no gas evolving, the strip visibly darkens or pits before it is submerged, or the rising bubbles behave as if heavier than air, pooling near the bottom instead of rising.
level_3: Bubbles appear only once the strip contacts the acid and rise continuously from the submerged strip toward the surface; the strip visibly shortens and thins while bubbling continues; the acid stays colorless and clear throughout; no solid residue, precipitate, or flame appears at any point.
level_4: Everything needed for a 3 is present, plus: bubbles form only on the submerged part of the strip, never on the tube's inner wall or in open liquid away from the metal; the strip's shrinkage is steady and one-directional, never appearing to regrow or freeze partway; no bubbles show up before the strip first touches the acid, and bubbling does not stop before the strip is essentially consumed or the clip ends.
level_5: Everything needed for a 4 is present, plus: the bubbles are rounded and roughly uniform rather than sheet-like or fused together; the strip's surface erodes evenly along its length rather than pitting unevenly in one spot; the liquid level in the tube stays essentially constant, with no overflow or visible evaporation; and there is no white fuming, smoke, or discoloration at the surface that would suggest a side reaction beyond magnesium displacing hydrogen from the acid.

Spatiotemporal Consistency rubric:
level_1: Severe continuity breaks: the strip appears inside the tube with no visible entry, the liquid vanishes and reappears, the tube snaps to a different rotation between shots, the room lighting jumps abruptly from one frame to the next, the strip's shape changes inconsistently mid-motion, or the camera cuts to a different angle or zoom with no transition.
level_2: Multiple noticeable continuity problems: the strip blinks in and out of view while being lowered, the liquid surface jumps around rather than settling smoothly, the shadow cast by the tube or strip jumps to a position inconsistent with the light source, the tube shifts as if bumped for no reason, or the strip's descent visibly skips or stutters more than once.
level_3: Small but noticeable rough edges: a slight jerk at the very start or end of the strip's descent, ripples on the liquid surface that don't quite match the timing of bubble emergence, or minor softening/sharpening of the shadow edge across frames, but the tube stays in one fixed place and orientation throughout, and nothing teleports, distorts, or breaks apart.
level_4: Everything needed for a 3 is present, plus: the strip's motion from hand to full submersion is smooth and unbroken; ripples on the liquid surface are explained entirely by bubbles breaking the surface, with no independent sloshing or trembling; the shadows stay tied to one steady overhead light source throughout; the strip is never shown partly hidden and then fully revealed without something actually causing that occlusion.
level_5: Everything needed for a 4 is present, plus: the first bubble appears essentially the instant the strip tip first touches the liquid surface, with no noticeable lag; the strip shortens at a steady, even pace rather than speeding up or slowing down erratically; the tube's walls keep the same visible thickness, curvature, and see-through clarity from the first frame to the last; and there is no flicker in brightness or color cast over the course of the clip.