The answer is AgCl or Silver Chloride. Silver chloride is a biological compound with the chemical formula of AgCl. This white crystal-like rock-solid is well recognized for its little solubility in water. Upon light or heating, silver chloride transforms to silver (and chlorine), which is gestured by greyish or purplish coloring to other samples.
The compound that could be separated by filtration after being mixed with water is AgCl (Silver Chloride) because it has low solubility in water. In contrast, CaCl₂, NaCl, and NiCl₂ are soluble and would not leave a solid residue. Thus, the best choice is AgCl.
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