Hydrogen peroxide oxidises [Fe(CN)₆]^4- to [Fe(CN)₆]^3- in acidic medium but reduces [Fe(CN)₆]^3- to [Fe(CN)₆]^4- in alkaline medium. The other products formed are, respectively :

When metal ‘M’ is treated with NaOH, a white gelatinous precipitate ‘X’ is obtained, which is soluble in excess of NaOH. Compound ‘X’ when heated strongly gives an oxide which is used in chromatography as an adsorbent. The metal ‘M’ is

The oxidation states of Cr in [Cr(H₂O)₆]Cl₃, [Cr(C₆H₆)₂] and K₂[Cr(CN)₂(O)₂(O₂)(NH₃)] respectively are :

The compound that does not produce nitrogen gas by the thermal decomposition is :