Reaction 1: PbCl2+K2CrO4→PbCrO4+2KCl
A = PbCrO4 (lead chromate)
Reaction 2: PbCrO4+4NaOH→Na2[Pb(OH)4]+Na2CrO4
B = Na2[Pb(OH)4] (sodium tetrahydroxoplumbate)
Reaction 3: PbSO4+4CH3COONH4→(NH4)2SO4+(NH4)2[Pb(CH3COO)4]
X = (NH4)2[Pb(CH3COO)4] (ammonium tetraacetatoplumbate)