Mohr's salt is a pale green crystalline solid which is soluble in water. It is a 'double sulfate' which contains two cations, one of which is Fe2+.The identity of the second cation was determined by heating solid mohr's salt with solid sodium hydroxide and a colourless gas was evolved. The gas readily dissolved in watdr giving an alkaline solution. A grey green solid residue was also formed which wasd insoluble in water. Whate are the identities of the gas and solid residue? A. Gas: H2 Residue: FeSO4 B.NH3 Na2SO4 C. NH3 Fe(OH)2 D. SO2 Fe(OH)2