Domain: Natural Science — Environmental Science
Target concept: Determination of Soil Potassium Content by Sodium Tetraphenylborate Colorimetry

Video generation prompt: Take 2 mL of potassium-containing soil extract into a test tube, add 2 drops of sodium tetraphenylborate solution, and shake thoroughly.

Evaluation guide:
(i) Target concept: Formation of a colloidal white precipitate via ion-specific complexation between K⁺ and B(C₆H₅)₄⁻ in aqueous solution.
Minimum mechanism: Presence of soluble K⁺ in extract; stoichiometric addition of tetraphenylborate anion; sufficient mixing to enable collision-driven nucleation; absence of interfering ions (e.g., NH₄⁺) or high ionic strength that would suppress precipitation.
(ii)Storyline: [Frame 0–1] Static shot: upright test tube with 2 mL pale-yellow soil extract visible (meniscus clear, no turbidity). [Frame 2–3] Dropper enters frame from top; two distinct drops detach sequentially into tube. [Frame 4–6] Hand grips tube and performs rapid rotational shake; liquid swirls visibly. [Frame 7–10] Liquid settles; uniform white turbidity emerges and persists across entire column, with no settling, no clearing, no color shift. Perspective: fixed frontal close-up; full test tube and hand region always in focus; no occlusion of liquid column during shake or observation.

Manual:
Experimental Procedure
1. Place a test tube containing 2 mL of potassium-containing soil extract.
2. Add exactly 2 drops of sodium tetraphenylborate solution using a calibrated dropper.
3. Cap and shake the test tube thoroughly for ~3 seconds.
Observation of Experimental Phenomena
A fine white turbidity or cloudiness appears uniformly throughout the liquid — no color change, no settling, no precipitation at bottom only.
Summary of Experimental Principles
Potassium ions react with sodium tetraphenylborate to form insoluble potassium tetraphenylborate, a white colloidal precipitate that causes measurable turbidity.

Prompt Grounding rubric:
level_1: No test tube present; no soil extract visible; no sodium tetraphenylborate solution bottle or dropper shown; no action of adding drops or shaking observed.
level_2: Test tube is present and contains a liquid, but the liquid is not labeled or visually identifiable as soil extract; sodium tetraphenylborate solution container is present but no dropper or drop delivery action occurs; no shaking motion is shown.
level_3: Test tube containing a clear-to-pale-yellow liquid is present; a dropper or bottle labeled/visually consistent with sodium tetraphenylborate solution is shown; exactly two discrete drops are delivered into the test tube; shaking motion (rotational or vigorous up-down agitation) of the test tube is performed.
level_4: All elements of score 3 are present AND the test tube is held upright before addition, remains upright during drop delivery, and is shaken immediately after addition; the dropper tip is visibly positioned directly above the test tube opening during delivery; no extraneous objects (e.g., gloves, labels, other reagents) obscure the core action sequence.
level_5: All elements of score 4 are present AND the two drops are delivered sequentially (not simultaneously), each drop is fully detached from the dropper tip before the next begins; shaking begins within the same continuous motion sequence as the final drop detachment; test tube orientation, grip, and motion path remain physically plausible and stable throughout, with no hand jitter, slip, or unnatural suspension.

Scientific and Causal Correctness rubric:
level_1: No color change occurs; liquid remains unchanged before and after addition and shaking; no precipitate forms; no turbidity or cloudiness appears at any point.
level_2: A color change occurs (e.g., to blue or green) but no precipitate forms; OR precipitate forms but without prior addition of reagent or without shaking; OR precipitate appears before drops are added.
level_3: After addition of two drops and thorough shaking, the originally clear-to-pale-yellow liquid develops uniform cloudiness or fine white turbidity; no other colors (e.g., pink, blue, brown) appear; no dissolution or clearing after shaking.
level_4: All elements of score 3 are present AND cloudiness/turbidity appears only after shaking completes (not during or before); turbidity is distributed evenly throughout the liquid column (not localized at bottom or surface only); no settling or layer separation observed within the video duration.
level_5: All elements of score 4 are present AND turbidity persists continuously until video ends; no transient clarity, no flickering opacity, no inconsistent particle density across the liquid volume; the visual texture of turbidity matches typical colloidal precipitate (fine, homogenous, non-granular, non-sedimented).

Spatiotemporal Consistency rubric:
level_1: Test tube disappears and reappears in different position/orientation; liquid level changes discontinuously without action; lighting shifts abruptly between frames; background or object edges show tearing, warping, or ghosting.
level_2: Test tube moves with teleportation (no visible motion path); dropper appears/disappears mid-action; shaking motion starts/stops with frame-level discontinuity; shadow on test tube jumps position without light source movement.
level_3: Test tube remains continuously visible in fixed position; all actions (drop delivery, shaking) occur as smooth, unbroken motions; lighting and shadows remain consistent in direction and intensity; no object clipping, morphing, or structural deformation.
level_4: All elements of score 3 are present AND camera viewpoint remains absolutely static (no pan, tilt, zoom, or drift); test tube base stays aligned with same horizontal plane throughout; hand motion follows biomechanically coherent trajectory (no inverted joints, impossible acceleration, or zero-inertia starts/stops).
level_5: All elements of score 4 are present AND inter-frame motion is perfectly fluid (no strobing, judder, or temporal aliasing); depth cues (e.g., parallax between hand and test tube, focus gradient) remain spatially consistent; no temporal mismatch between action onset (e.g., dropper lowering) and effect onset (e.g., drop contact).