Domain: Healthcare — Nutrition & Dietetics
Target concept: The Effect of Vitamin C on Iron Absorption (Simulation)

Video generation prompt: Pour iron solution into two transparent cups. Add vitamin C solution to one cup and leave the other unchanged. Stir both cups separately with a pipette. Use simple experimental equipment, transparent liquids, and perform the procedure in sequence, focusing on the addition and mixing of the solutions.

Evaluation guide:
(i) Target concept: Redox-mediated solubility enhancement of dietary iron by ascorbic acid.
Minimum mechanism: Iron solution must contain Fe³⁺ species (e.g., ferric chloride) that undergo reduction to Fe²⁺ upon vitamin C exposure. Fe³⁺ is the more strongly colored, hydrolysis-prone species in water (a yellow-brown solution that can turn slightly hazy), while Fe²⁺ is comparatively pale and far less prone to hydrolysis; reduction therefore produces a perceptible, stable optical difference in the vitamin-C cup, a paler hue and reduced cloudiness (improved clarity), relative to the untreated cup, which keeps its original darker, slightly hazier appearance.
(ii)Storyline: Frame 0–1: Static wide shot showing two empty transparent cups side-by-side. Frame 2–3: Simultaneous or sequential pouring of iron solution into both cups; liquid must fill to identical level. Frame 4: Vitamin C solution dispensed *only* into left cup, visible as distinct droplet stream or labeled reagent. Frame 5–6: Pipette enters left cup, stirs with circular motion, exits cleanly. Frame 7–8: Pipette re-enters right cup, stirs with separate circular motion, exits cleanly. Frame 9–10: Final static hold; both cups remain in frame, side-by-side, with unambiguous visual contrast sustained. Perspective: Fixed frontal orthographic view, eye-level, full cup height visible; no occlusion; background neutral and non-distracting.

Manual:
Experimental Procedure
1. Place two identical transparent cups side-by-side on a flat surface.
2. Pour equal volumes of iron solution into both cups.
3. Add vitamin C solution to only the left cup.
4. Stir the left cup with a pipette until homogeneous.
5. Stir the right cup with the same pipette until homogeneous.
Observation of Experimental Phenomena
The left cup (with vitamin C) becomes noticeably paler as its original yellow-brown color fades and any haziness clears; the right cup (untreated) keeps its darker yellow-brown color and stays slightly cloudy.
Summary of Experimental Principles
Vitamin C (ascorbic acid) reduces ferric iron (Fe³⁺) to ferrous iron (Fe²⁺). Fe³⁺ is the more strongly colored, hydrolysis-prone species in water — it tends to form pale yellow-brown to orange hydroxide complexes that can cloud the solution — while Fe²⁺ is comparatively pale and much less prone to hydrolysis under these mildly acidic conditions. Reducing Fe³⁺ to Fe²⁺ therefore lightens the color and improves clarity, and this same reduced, more soluble form of iron is also the form more readily absorbed by the body.

Prompt Grounding rubric:
level_1: No transparent cups are shown; no iron solution or vitamin C solution appears; no pipette is used; no pouring or stirring action takes place at all; nothing in the clip resembles the described setup.
level_2: At least one transparent cup with liquid appears, but either: both cups look completely identical throughout with nothing added to either one; or vitamin C solution is never added to any cup; or a pipette appears but is never used to stir; or liquid is poured into only one cup instead of both, or into a container that is not a cup.
level_3: Two transparent cups sit side by side; iron solution is poured into both; vitamin C solution is then added to exactly one of the two cups (never both, never neither); a pipette is used to stir each cup on its own; pouring the iron solution, adding the vitamin C, and stirring each cup happen roughly in that order.
level_4: All conditions for score 3 are met; in addition, the two cups stay in the same adjacent spots for the whole clip; the pipette actually dips into and stirs the liquid in both cups rather than hovering above it; the vitamin C solution looks visually distinct from the iron solution (different color, or a labeled dropper) and goes into only the designated cup before either cup is stirred.
level_5: All conditions for score 4 are met; in addition, the vitamin C solution lands only in its intended cup, with no drips or splashes reaching the other cup or the table; the pipette stirs each cup with its own separate stirring motion rather than one continuous stir spanning both cups; the iron solution is poured into both cups before any vitamin C is added; nothing unexpected enters or leaves the shot, and the whole sequence plays out in one continuous take without cutting away or repositioning the camera.

Scientific and Causal Correctness rubric:
level_1: Neither cup changes color or clarity at all after stirring; or both cups end up looking identical; or the untreated cup is the one that visibly lightens and clears while the vitamin-C cup stays unchanged (the reverse of the expected effect); or any visible change happens before the vitamin C is even added.
level_2: One cup does change after stirring, but the direction or timing is off: the change happens in the untreated cup rather than the vitamin-C cup; or the two cups change by the same amount so no contrast develops between them; or a change appears immediately upon pouring the iron solution, before vitamin C is added or before either cup is stirred.
level_3: After stirring, a clear contrast develops between the two cups: the vitamin-C cup becomes noticeably paler in color and any cloudiness in it clears up, while the untreated cup keeps its original darker yellow-brown color and any haziness it had; this contrast appears only after the stirring is finished and stays visible until the end of the clip.
level_4: All conditions for score 3 are met; in addition, the lightening and clearing is confined to the vitamin-C cup only, with no fading or clearing in the untreated cup; the untreated cup's darker color and any cloudiness stay steady with no drifting or flickering; both cups keep a level of transparency believable for a water-based solution throughout.
level_5: All conditions for score 4 are met; in addition, the contrast between the two cups is visible immediately once stirring stops and stays visible without fading, flickering, or being washed out by glare all the way to the end of the clip; the untreated cup's color and clarity at the end match what it looked like right after the iron solution was first poured in, with no unexplained additional change.

Spatiotemporal Consistency rubric:
level_1: A cup or the pipette disappears and reappears, or jumps to a new spot, between frames; the liquid level in a cup changes suddenly with no visible pouring to explain it; the room lighting flips abruptly from bright to dark, or the reverse, within a single frame; a cup's shape visibly bends or warps; the background behind the cups disappears or tears apart.
level_2: One cup is briefly blocked from view and reappears shifted from its earlier position; the pipette's movement skips or freezes for more than a frame at a time; the liquid surface sloshes or shears in a way that doesn't match the stirring motion shown; a shadow on a cup or the pipette changes shape abruptly with no matching change in the light or the object's position; something in the background flickers in and out.
level_3: The two cups stay in the same left-right spots relative to each other throughout; the pipette moves between the cups along a visible path rather than jumping from one to the other; the liquid surface only shows the kind of gentle ripple that stirring would produce, with no splashing or liquid floating above the rim; the room's light source stays put, so shadows on the cups and pipette keep pointing the same direction from start to finish; neither cup nor the pipette visibly cracks, bends, or comes apart.
level_4: All conditions for score 3 are met; in addition, the pipette's motion speeds up and slows down smoothly rather than jerking; the stirring path in one cup never crosses into or overlaps with the stirring path in the other; the liquid surface (meniscus) stays intact and doesn't break apart or blur during pouring or stirring; no cup or pipette edge blurs or smears in a way that hides its outline.
level_5: All conditions for score 4 are met; in addition, reflections and highlights on the cups' surfaces shift in a way that matches the camera and light position rather than floating independently; stirring only disturbs the liquid locally and briefly, with no liquid splashing over the rim or swirling on long after the pipette stops moving; no frame repeats, freezes, or stutters anywhere in the clip; both cups' edges and the liquid surfaces inside them stay sharp and easy to make out in every frame.