A metal gives two chlorides ‘A’ and ‘B’. ‘A’ gives black precipitate with NH4OH and ‘B’ gives white. With KI ‘B’ gives a red precipitate soluble in excess of KI. ‘A’ and ‘B’ are respectively :
Hg2Cl2 and HgCl2
'A' is Hg2Cl2 and 'B' is HgCl2
HgCl2+2KI→HgI2+2KCl
Red
HgI2+2KI→K2HgI4Soluble