Domain: Natural Science — Earth Science
Target concept: Ion-exchange resin column, showing the color front formed by the replacement of hard water ions for sodium ions

Video generation prompt: A transparent vertical column is filled with sodium-type ion-exchange resin and a color indicator; hard water, rich in calcium, is poured in at the top and flows downward through the column.

Evaluation guide:
(i) Target concept: Ion-exchange-driven color front propagating down a fixed-bed column as Ca2+ from hard water displaces Na+ on the resin and binds a co-located metal-ion indicator.
Minimum mechanism: Resin must be functional and initially in the Na-form; a metal-ion-sensitive color indicator (responsive to Ca2+/Mg2+ binding, not to pH, since a Na+/Ca2+ swap is a charge-balanced exchange of two non-hydrolyzing cations and does not by itself alter local pH) must be co-located within the resin matrix rather than dissolved in the flowing water; hard water must supply exchangeable Ca2+; flow must be laminar and downward to sustain a sharp front geometry.
(ii)Storyline: Frame 0–2: Static column showing uniform indicator color throughout resin bed. Frame 3–5: Hard water enters top; color front initiates at top interface. Frame 6–8: Front advances downward as a continuous, horizontal band, sharply separating two uniform-color zones. Frame 9–10: Front reaches mid-column; no reversal, diffusion, or branching. Viewpoint: Fixed frontal orthographic view, column centered, full height visible, no obstructions, consistent lighting.

Manual:
Experimental Procedure
1. Fill a transparent vertical column with sodium-type ion-exchange resin beads pre-equilibrated with a metal-ion-sensitive color indicator (analogous to Eriochrome Black T, which binds Ca²⁺/Mg²⁺).
2. Pour hard water (Ca²⁺-rich) slowly into the top opening.
3. Observe downward movement of a sharp horizontal color front through the resin bed.
Observation of Experimental Phenomena
A distinct, horizontally aligned color boundary forms and migrates downward steadily as hard water flows through the column; the region above the front, already reached by the incoming hard water, displays the exchanged-color state (e.g., yellow), while the region below the front, not yet reached, retains the original indicator color (e.g., blue).
Summary of Experimental Principles
Calcium ions in hard water displace sodium ions bound to the resin. The calcium ions bind directly to the metal-ion-sensitive indicator co-located in the resin, producing a distinct color-complex change — independent of any pH shift — that is visualized as a propagating front.

Prompt Grounding rubric:
level_1: No vertical transparent column visible; no ion-exchange resin present; no color indicator visible; no hard water inflow shown; none of the four core elements (column, resin, indicator, hard water) appear together.
level_2: A transparent tube is visible, but the setup is materially incomplete: the granular fill is absent or clearly not a resin (e.g., loose powder or a plain liquid), the color indicator is nowhere visible, or no hard water is shown entering the top.
level_3: The transparent column is filled with a visibly granular resin bed; a color indicator is visible somewhere within it; hard water can be seen entering at the top with a corresponding downward flow inside the column; column, resin, indicator, and incoming water all appear together in a coherent single scene.
level_4: Everything required for a 3 holds, and in addition: the resin clearly forms one continuous packed bed rather than scattered particles or a suspension; the indicator color is spread evenly through the bed before the hard water begins entering; the hard water enters only at the top (any outflow only at the bottom); no hand, label, or unrelated equipment covers the column.
level_5: Everything required for a 4 holds, and in addition: the column fills at least roughly three-quarters of the frame's vertical extent; the resin bed runs continuously from bottom to near-top with no visible gaps or trapped air pockets; the indicator color stays confined to the resin bed rather than floating loose in the water above it; the incoming hard water forms a single steady downward stream with no splashing, side leaks, or a second bypass stream running around the resin.

Scientific and Causal Correctness rubric:
level_1: No color front forms at all: the resin's color stays uniform through the whole run, or new color appears at random scattered spots instead of as one moving boundary, or the color shifts before any hard water has entered the column.
level_2: A patch of new color appears but fails to travel through the bed: it stays confined to the very top or very bottom instead of advancing, or a front seems to move upward, or the color change happens ahead of where the incoming water has actually reached.
level_3: A single, sharp, roughly horizontal color boundary appears within the resin bed and visibly moves downward as hard water keeps entering; the zone the front has already crossed shows one color and the zone still ahead of it shows a different color; the boundary sits clearly lower in a later frame than in an earlier one.
level_4: Everything required for a 3 holds, and in addition: the boundary stays sharp rather than smearing into a wide, fuzzy gradient (any blurred transition stays much narrower than the distance the front has already traveled), and each of the two color zones stays internally uniform, with no fading back toward the original color or stray patches within a zone.
level_5: Everything required for a 4 holds, and in addition: the boundary stays visibly horizontal across the full width of the column throughout its descent, tilting no more than about 5° from level; no color appears in the free-flowing water above or below the resin bed; a region that has changed color never fades or reverts; the contrast between the two zones stays strong and even across the whole column width for the entire descent.

Spatiotemporal Consistency rubric:
level_1: The column, resin, or incoming water stream appears or vanishes abruptly between frames; the resin bed jumps to a different vertical position; the color front leaps downward by more than half the column's height in a single cut; the lighting suddenly flips violently (e.g., a flash or a sudden blackout) with no cause; the whole column suddenly tilts out of vertical or rotates.
level_2: Smaller but still visible breaks: the resin bed shifts noticeably within the frame with no flow event to explain it; the color front flickers on and off across a few consecutive frames instead of holding steady; the incoming water stream stops and restarts with no visible cause; the column's outline warps or wobbles.
level_3: The column stays fixed in the frame; the resin bed keeps a stable position and grainy texture; the color front descends smoothly with no jumps, freezes, or reversals; the incoming water stream flows continuously with a steady width and clarity; there is no unexplained flicker in the lighting on the column.
level_4: Everything required for a 3 holds, and in addition: the resin's granular texture stays consistent, with no melting, dissolving, or swelling; the water stream keeps a constant width and clarity from entry point to where it's absorbed; the front's edge stays geometrically consistent, without bending, tilting, or splitting into multiple boundaries, as it moves.
level_5: Everything required for a 4 holds, and in addition: the sequence shows smooth, continuous motion with no duplicated, skipped, or obviously interpolated-looking frames; no motion blur hides the front's edge or the resin's grain; the column never drifts relative to the background; no glare or reflection appears that hides the resin bed or the color front.