What is primary and secondary valency of Pt in [Pt(NH₃)₆]Cl₄? 

4,6

Primary valencies are satisfied by anions only. The number of primary valencies depend upon the oxidation state of central metal.

Secondary valencies are satisfied by the ions or the neutral electron pair donor molecules.

[Pt(NH₃)₆]Cl₄ : [Pt(NH₃)₆]⁴⁺ + 4Cl^- 

Primary valency : 4 satisfied by Cl^-

Secondary valency : 6 satisfied by NH₃ electron pair donor molecules.