K2[PtCl4] is a coordination compound with complex ion [PtCl4]2−.
When K2[PtCl4] is dissolved in water, the complex ion [PtCl4]2− will retain its identity.
K2[PtCl4]→2K++[PtCl4]2−
However when AgNO3 is added to K2[PtCl4], grey precipite of PtCl2(AgNO3)(S) is obtained.
K2PtCl4+2AgNO3→2KCl(aq)+PtCl2(AgNO3)(S)