Nickel carbonyl Ni(CO)4,colourless, flammable, poisonous liquid boiling at 430C;soluble  in alcohol and concentrated nitric acid; insoluble in water; used in gas plating (vapour decomposes at 600C) and to produce metallic nickel. Also known as nickel tetracarbonyl.

Nickel cyanide
Ni(CN)₂.4N₂O, poisonous, water-insoluble apple-green powder; melts and loses water at 2000C, decomposes at higher temperature; used for electroplating and metallurgy.

Niobic acid
Nb₂O5.nH₂O, family of hydrates; white precipitate, soluble in inorganic acids and bases, insoluble in water; its formation is part of the analytical determination of niobium.

Nickel nitrate
Ni(NO₃)2.6H₂O, fire-hazardous oxidant; deliquescent, green, water-and alcohol-soluble crystals; used for nickel plating and brown ceramic colours, and in nickel catalysts.

Nickel oxide
NiO, green powder; soluble in acids and ammonium hydroxide; insoluble in water; used to make nickel salts and for porcelain paints. Also known as green nickel oxide; nickelous oxide.

Nickel silver
A group of alloys of copper, zinc and nickel in ranging proportions.