Domain: Natural Science — Environmental Science
Target concept: Determination of Chloride Content in Irrigation Water (Silver Nitrate Colorimetric Method)

Video generation prompt: Take 2 mL of an irrigation water sample containing chloride ions into a test tube and add 2 drops of silver nitrate solution.

Evaluation guide:
(i) Target concept: Visual confirmation of chloride-induced AgCl precipitation via controlled reagent addition.
Minimum mechanism: Silver nitrate solution must be dispensed as discrete droplets into a static aqueous chloride-containing sample; Ag⁺ and Cl⁻ ions must achieve molecular contact; nucleation and growth of AgCl colloids must occur rapidly enough to be visually resolved within 10 seconds; colloid size must exceed Rayleigh scattering threshold to produce visible turbidity.
(ii)Storyline: [Frame 0] Static shot: upright test tube with ~2 mL clear liquid. [Frame T1] Dropper enters top of frame, vertically aligned over test tube mouth. [Frame T2] First droplet detaches, falls, and immerses: localized turbidity appears at impact site. [Frame T3] Second droplet detaches; first turbidity expands downward. [Frame T4] Second droplet immerses: turbidity intensifies and homogenizes. [Frame T5–end] Stable white cloudy suspension fills liquid column; no settling, clearing, or discoloration. Perspective: Fixed frontal close-up (test tube occupies 60–80% height), shallow depth-of-field isolating tube/dropper, even front lighting to maximize precipitate visibility.

Manual:
Experimental Procedure
1. Place a clean test tube on surface.
2. Use a dropper to draw silver nitrate solution.
3. Add exactly 2 drops of silver nitrate solution into 2 mL of irrigation water sample in the test tube.
Observation of Experimental Phenomena
White cloudy precipitate forms immediately upon addition of silver nitrate solution.
Summary of Experimental Principles
Chloride ions in water react with silver nitrate to form insoluble white silver chloride precipitate: Cl⁻ + Ag⁺ → AgCl↓.

Prompt Grounding rubric:
level_1: No test tube is visible in frame; no clear liquid sample is present; no silver nitrate dropper or bottle appears; the video shows no moment of liquid entering the test tube from a dropper.
level_2: A test tube holding a clear liquid appears, but its fill level looks far off from 2 mL (either filled almost to the rim or nearly empty); a dropper or small reagent bottle is visible near the tube, but no droplet is ever seen leaving its tip and entering the liquid.
level_3: A test tube with a clear liquid sits upright in frame; a dropper containing a clear/pale liquid is held above the tube's mouth; exactly two separate droplets leave the dropper tip and fall into the test tube; no unrelated glassware (extra beaker, second test tube, measuring cylinder) appears in the shot.
level_4: Everything in the 3-point description holds, and in addition the liquid level in the test tube sits low, around the bottom third of the tube (consistent with a small ~2 mL volume rather than a half-full or brimming tube); the dropper releases precisely two separate droplets, not a single blob or a thin stream; both droplets land inside the tube opening rather than on the rim or missing the tube; no gloved hand, printed label, or other lab clutter competes for visual attention in the frame.
level_5: Everything in the 4-point description holds, and in addition the test tube reads as a plain, unlabeled cylindrical glass tube of ordinary lab size; the dropper is recognizable as a slim glass pipette with a rubber bulb top; the liquid inside the dropper looks clear/colorless (real aqueous silver nitrate solution is not amber-tinted; any brown glass shown belongs only to a light-blocking storage bottle, never to the solution itself); both droplets are clearly rounded and separate as they fall, with neither droplet count nor landing spot obscured by blur.

Scientific and Causal Correctness rubric:
level_1: The test tube liquid shows no color or clarity change at any point in the clip; it stays fully transparent and colorless from start to end; no cloudy or solid material ever forms; nothing in the tube visually reacts to the added drops.
level_2: Some visible change happens in the tube, but it's the wrong kind: for example a blue, green, or yellow tint, or a uniform pink liquid, instead of a white cloudy precipitate; or a lumpy/gelatinous clump forms instead of fine white cloudiness; or the cloudiness or color is already present before any droplet lands, or lingers with no visible connection to the droplets landing.
level_3: After both silver nitrate droplets have entered the liquid, a white, cloudy precipitate (silver chloride) becomes visible within the sample; the surrounding liquid itself stays colorless; the precipitate is not present before the droplets arrive and first appears near where the droplets hit the surface.
level_4: Everything in the 3-point description holds, and in addition the white precipitate looks like a fine, even cloudiness rather than large chunky clumps or stringy flocs; the cloudiness visibly increases after the second droplet lands, not just after the first; the liquid never clears back up or redissolves the precipitate; no brown or yellow staining appears on the tube walls or in the liquid.
level_5: Everything in the 4-point description holds, and in addition the white particles stay suspended through the whole clip rather than settling into a layer at the bottom; the cloudiness looks roughly even throughout the liquid column once both droplets have been added; there is no shiny film, rainbow sheen, or surface ring on top of the liquid; visible turbidity begins within roughly a second of each droplet touching the liquid, without a noticeably longer delay.

Spatiotemporal Consistency rubric:
level_1: The test tube vanishes from the shot and then reappears at a different spot with no visible motion connecting the two; the dropper instantly relocates from one position to another without traveling between them; the room lighting suddenly flips (e.g. from bright to dim) partway through; the liquid's surface jumps to a different height with no visible cause; the clip stutters or skips hard enough to break the sense of continuous action.
level_2: The test tube tilts or spins in ways that don't match anyone touching it; the dropper's path toward the tube mouth veers sideways or curves oddly instead of moving straight down; ripples on the liquid surface don't match up with when a droplet actually lands; the white precipitate appears spread through the whole liquid column all at once, instead of first showing up where the droplet landed and then spreading from there.
level_3: The test tube stays in the same spot on the surface throughout the clip; the dropper moves straight down toward the tube's mouth without drifting sideways; the two droplets leave the dropper tip one after the other, with the first one fully separating before the second one starts forming; the precipitate first shows up at the point of droplet impact and then gradually spreads downward through the liquid.
level_4: Everything in the 3-point description holds, and in addition the camera framing never pans, tilts, or zooms during the clip; the lighting on the tube and liquid stays even, without shadows sliding around or the scene suddenly brightening or dimming; the liquid surface dips and settles smoothly each time a droplet lands, rather than jumping or freezing; the spreading precipitate looks like it's diffusing loosely through the liquid rather than shooting out in a rigid ring or a directional jet.
level_5: Everything in the 4-point description holds, and in addition the droplet visibly narrows and pinches off from the dropper tip before falling; because the dropper is held straight above the tube mouth, each droplet drops essentially straight down rather than curving sideways in an arc; the liquid surface shows one small rebound right after each droplet lands; the precipitate begins right at the droplet's entry point and spreads outward roughly evenly in all directions, without a lopsided bias to one side.