Domain: Natural Science — Chemistry
Target concept: Addition reaction of ethylene with bromine water

Video generation prompt: A test tube contains 10 mL of orange-yellow bromine water, into which ethylene gas is introduced.

Evaluation guide:
(i) Target concept: Electrophilic addition of Br₂ across C=C bond in ethylene, resulting in quantitative decolorization of bromine water.
Minimum mechanism: Bromine (Br₂) must be molecularly dissolved in water (yielding orange-yellow solution); ethylene gas must make direct contact with aqueous Br₂; reaction must proceed stoichiometrically to consume Br₂, eliminating its characteristic color.
(ii)Storyline: Frame 0–1: Static shot of upright test tube with orange-yellow liquid filling lower portion; clear meniscus and glass refraction visible. Frame 2–3: Gas delivery tube enters frame and makes contact with liquid surface (tip submerges). Frame 4–7: Continuous stream of uniform spherical bubbles emerges from tube tip; simultaneous, progressive, and uniform decolorization spreads from bubble contact zone upward and outward until entire liquid volume is colorless. Frame 8–10: Final colorless state stabilized; no residual color, no bubbles exiting surface; tube remains submerged and stationary; consistent lighting and perspective maintained throughout.

Manual:
Experimental Procedure
1. Place a clean test tube containing 10 mL of orange-yellow bromine water on stand.
2. Insert gas delivery tube into the bromine water.
3. Introduce ethylene gas through the tube for ~5 seconds.
Observation of Experimental Phenomena
The orange-yellow color of bromine water completely fades to colorless during gas introduction.
Summary of Experimental Principles
Ethylene undergoes electrophilic addition with bromine (Br₂) dissolved in water, forming colorless 1,2-dibromoethane — confirming unsaturation via decolorization.

Prompt Grounding rubric:
level_1: No test tube is visible; there is no orange-yellow liquid present; there is no sign of ethylene gas being introduced; no container holding the bromine water appears; the clip does not depict any reaction setup.
level_2: A transparent container is present, but its contents are colorless or blue-tinted rather than orange-yellow; the introduction of ethylene gas is only implied by on-screen text or sound, with no gas-delivery tube shown touching the liquid; there is no visible interaction between any gas and the liquid.
level_3: A single transparent test tube holding orange-yellow liquid is clearly visible; a gas delivery tube enters through the top opening of the test tube; the tube's tip sits at or just above the liquid surface; no other container or reagent appears in frame; the sequence shows the tube followed by the start of gas delivery.
level_4: In addition to everything already covered at score 3: the gas delivery tube stays in the same position relative to the test tube for the whole clip; the test tube remains upright and does not move; the orange-yellow liquid fills roughly the lower half to two-thirds of the tube; no extraneous object (label, hand, other glassware) enters frame during gas delivery.
level_5: In addition to everything already covered at score 4: the gas delivery tube's tip is shown submerged inside the orange-yellow liquid, keeping contact with the liquid for at least three consecutive frames; the test tube is framed centrally and vertically; nothing crops, occludes, or distorts the view of the tube or the liquid inside it.

Scientific and Causal Correctness rubric:
level_1: The liquid stays orange-yellow for the entire clip; no decolorization happens at all; the liquid's clarity never changes; there is no visible link between the gas entering and any change in the liquid's color.
level_2: The color starts to change but never finishes: fading shows up only right at the tube wall or liquid surface while orange-yellow still covers more than 70% of the visible liquid; the fading is patchy rather than an overall shift; the liquid keeps enough of its yellow-orange cast that it would not read as decolorized.
level_3: The orange-yellow liquid visibly turns colorless (or pale yellow at most) across its whole visible volume; the change only begins after gas delivery has started and continues progressively from there; by the end, the liquid is uniformly colorless with no orange-yellow patch remaining; no precipitate, extra bubbling, or layer separation accompanies the change.
level_4: In addition to everything already covered at score 3: the color change tracks the gas delivery in time; the first visible fading appears within about a second of the tube tip contacting the liquid or gas beginning to flow; the fading is neither noticeably delayed nor already underway before gas starts; once colorless, the liquid stays that way for the rest of the clip.
level_5: In addition to everything already covered at score 4: the fading spreads outward from where the gas enters the liquid and reaches every part of the liquid without leaving any visible patch of remaining orange-yellow color in the tube; the whole liquid ends up the same shade of colorless (or pale yellow) with no localized variation; no intermediate color such as green or brown appears at any point during the fade.

Spatiotemporal Consistency rubric:
level_1: Between two frames, the test tube's position or orientation changes abruptly with no motion shown carrying it there; the liquid's surface level jumps without any pouring action; the gas delivery tube blinks in and out of frame; the overall lighting swings abruptly from bright to dark to bright again; or there are visible cuts, jumps, or duplicated frames.
level_2: The test tube wobbles hard or spins more than roughly 30 degrees with nothing shown causing it; the liquid surface keeps waving up and down long after it should have settled; the gas tube bends or warps in a way glass or rubber tubing physically couldn't; or the room's light level flickers rapidly for no visible reason.
level_3: The test tube stays upright and fixed in the same spot the whole time; the liquid surface stays level and calm except for small ripples that appear only where gas bubbles are actually breaking the surface; the gas delivery tube holds one rigid, unchanging position and angle; the shadow the gas delivery tube casts at the moment its tip first touches the liquid falls on the same side as the shadow it casts once bubbling and decolorization are complete, rather than switching sides partway through.
level_4: In addition to everything already covered at score 3: ripples on the liquid surface show up only while gas bubbles are actually emerging and settle back down within a couple of frames after the last bubble; no lingering ripple outlasts the bubbling; the camera framing does not drift, so the tube and background stay in the same relative position; the tube's outline and the liquid's meniscus line up frame to frame with no visible misalignment.
level_5: In addition to everything already covered at score 4: every bubble forming at the tube tip stays fully inside the liquid before rising, keeping a round shape and a consistent size range, with none clipped at the top edge; the curve of the liquid's surface stays smooth and unbroken throughout; the tube and the liquid boundary hold their position steadily from one frame to the next with no visible skipping or misalignment.