daily tips and question for ICSE PHYSICS AND CHEMISTRY

A reddish brown solid quickly becomes moist on exposure to air. When dissolved in water it gives a pale yellow solution. On adding sodium hydroxide to a portion of solution we obtain a reddish brown precipitate. On adding silver nitrate solution to a solution of the solid we obtain a thick curdy precipitate insoluble in dilute nitric acid but soluble in ammonium hydroxide solution.
Why does the solid become moist on exposure to air?
Name the reddish brown precipitate.
Why did the thick curdy precipitate not look white?
What is the anion and cation in the soluble of the powder?
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