Domain: Natural Science — Chemistry
Target concept: Hydrogen evolution corrosion of steel

Video generation prompt: A nail is immersed in a sodium chloride solution acidified with dilute hydrochloric acid.

Evaluation guide:
(i) Target concept: Hydrogen evolution corrosion of steel (iron) in acidic chloride electrolyte.
Minimum mechanism: Presence of conductive aqueous medium containing H+ (from HCl) and Cl- (from NaCl); electrochemical anodic dissolution of Fe coupled with cathodic H2 evolution at the metal surface, releasing Fe2+ into the acidic solution rather than depositing rust on the metal; Cl--induced localized breakdown of any protective oxide layer enabling sustained reaction at the submerged interface.
(ii)Storyline: [Frame 0-2] Nail positioned above liquid surface in beaker; [Frame 3-4] Nail begins descending vertically into solution; [Frame 5-10] Nail comes to rest partially submerged, with its lower portion below the liquid surface and its upper portion remaining visible above it -- immediate onset of many small gas bubbles nucleating and rising continuously from the submerged metal surface only; the submerged surface gradually dulls and roughens compared with the untouched surface above the liquid line, while the solution itself stays clear or takes on at most a faint pale yellow-green tint from dissolved iron ions; the liquid-air interface remains sharply defined with a stable meniscus; all events occur within a fixed frontal viewpoint showing the full nail length and upper beaker region; no extraneous motion, tools, or environmental interference.

Manual:
Experimental Procedure
1. Place a clean iron nail into a transparent glass beaker.
2. Pour colorless sodium chloride solution acidified with dilute hydrochloric acid into the beaker until the nail is partially submerged, leaving its upper portion above the liquid surface.
Observation of Experimental Phenomena
1. Continuous evolution of colorless gas bubbles on the submerged surface of the nail.
2. Gradual dulling and roughening of the submerged metal surface, with the solution staying clear or taking on at most a faint pale yellow-green tint from dissolved iron ions, rather than an orange-brown rust coating forming on the nail.
Summary of Experimental Principles
Acidified NaCl solution provides H+ ions and Cl- ions, accelerating electrochemical hydrogen evolution corrosion of iron: Fe -> Fe2+ + 2e- (anode), 2H+ + 2e- -> H2 (cathode). Cl- promotes breakdown of the passive oxide layer, and the dissolved Fe2+ remains in solution under these acidic conditions instead of precipitating as rust on the nail.

Prompt Grounding rubric:
level_1: No nail appears; no beaker or transparent container appears; no liquid is visible; nothing resembling an acidified sodium chloride solution appears; the nail, container, and liquid never appear together in the same shot.
level_2: Only some of the required objects appear together -- for example a nail with no container, or a container of liquid with no nail -- but nail, container, and liquid are never all visible at once; the nail is never shown entering or resting in the liquid.
level_3: The nail, a transparent container, and a liquid are all visible together in the same shot, and the nail sits at or below the liquid surface; but the liquid does not read as a clear aqueous solution -- for instance it lacks a visible meniscus or looks syrupy, cloudy, or otherwise unlike water -- or there is no visual cue (label, clarity, colorlessness) suggesting it is a saline/acid solution rather than something else.
level_4: The nail, a transparent container, and a colorless, clear liquid all appear together; part of the nail is submerged below the liquid surface while another part remains visibly above it; the container is not warped or oddly transparent; the liquid shows a visible meniscus and reflects light the way water does; no distracting extra objects such as gloves, printed labels, or droppers dominate the frame.
level_5: The nail sits inside a standard-looking cylindrical glass beaker filled to roughly half to two-thirds of its height with a colorless, clear liquid; the nail is positioned so its lower portion is submerged and its upper portion remains clearly visible above the liquid surface; the liquid shows a natural meniscus and surface reflections; no extra objects, text, or labels appear anywhere in the shot; the camera holds one fixed, centered view of the immersion zone for the whole clip.

Scientific and Causal Correctness rubric:
level_1: No sign of any reaction appears -- no bubbles, no change to the nail's surface, no change to the liquid -- the nail stays shiny and the liquid stays perfectly still and clear the whole time; or a rust-colored coating appears on the nail instead of the expected bubbling and surface dulling.
level_2: Bubbles appear somewhere in the shot but are not attached to or rising from the nail's surface; or bubbles only show up after the nail has been pulled back out of the liquid; or the nail's exposed (dry) portion above the waterline changes appearance instead of the submerged portion; or the liquid changes color with no visible connection to the nail.
level_3: Small gas bubbles form and cling to or rise from the submerged part of the nail while it is underwater; bubble size and spacing look uneven but plausible; the submerged metal looks slightly duller or rougher than the dry portion above the surface; no bubbling or surface change happens on the part of the nail above the liquid.
level_4: Bubbles form continuously and only on the submerged part of the nail throughout the immersion; the submerged surface grows visibly duller and more matte over time compared with the untouched portion above the waterline; the dry portion of the nail shows no bubbling or surface change; the liquid stays clear, at most taking on a very faint tint, with no rust-colored film forming anywhere on the nail.
level_5: Bubbles begin as soon as the nail is fully submerged and continue steadily only on the submerged surface; that surface's dulling/etching progresses gradually and is confined by a sharp line right at the liquid surface, with no change above it; the liquid stays clear or develops only a faint pale yellow-green cast consistent with dissolved iron, never a rust-colored film or opaque cloudiness; no bubbling, dulling, or color change ever appears on the dry part of the nail.

Spatiotemporal Consistency rubric:
level_1: The nail or beaker disappears and reappears between shots; the liquid's surface level changes with no pouring or descent action shown; the lighting flips abruptly from one frame to the next; the nail moves or rotates without any visible motion connecting the two positions; the beaker wall shows a sudden crack or gap with no cause.
level_2: The nail's position shifts by more than a centimeter between frames with no visible motion carrying it there; the liquid surface flickers or changes shape inconsistently frame to frame; a shadow on the nail or beaker changes direction without any corresponding change in the light source; the nail partly disappears behind the beaker's edge and comes back with a different tilt.
level_3: The nail, beaker, and liquid keep the same relative positions and sizes throughout the clip; the nail's descent into the liquid, if shown, is a single smooth, continuous motion rather than a jump; the light source and the resulting highlights on the glass stay in the same place and strength across the clip; the liquid surface rises and settles smoothly without oscillating or splashing unnaturally.
level_4: Everything required for score 3 holds, and in addition: the nail travels downward with unbroken, continuous motion until it is fully submerged; the liquid surface rises evenly and forms a stable meniscus with no jitter or warping in the container's shape; reflections on the beaker walls and liquid surface shift only in ways consistent with the fixed camera viewpoint.
level_5: Everything required for score 4 holds, and in addition: the nail descends in a straight vertical path at a roughly constant speed until fully submerged, with no pause, wobble, or backward motion; the liquid surface rises without ripples, splashing, or bounce-back; the meniscus settles into its final shape smoothly; every reflection and highlight on the glass and liquid changes in a way consistent with a still light source and fixed camera throughout.