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1. 

   3-18-11

   guest says:

   Potassium dichromate

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2. 

   2-29-12

   guest says:

   Silver (Ag) is the element used in negatives and black-and-white films and turns black in light. Initially, the silver is in the form of a metallic salt (e.g., AgNO3) and is converted to metallic silver (Ag) when the negative or black-and-white film is developed. The metallic silver (Ag) absorbs all visible frequencies of light and thus appears black because no frequencies of the visible light spectrum are reflected.

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