Chapter 20 - Chemistry of Selected Transition Elements and Coordination Compounds - Questions for Review and Thought - Topical Questions - Page 893b: 49a

4

Coordination number is equal to the number of coordinate covalent bonds to the central $Pt^{2+}$ ion. en (ethane-1,2-diamine) is a didentate ligand, i.e., it can bind through two donor atoms. There are two en ligands in this coordination compound. Therefore, coordination number= $2\times2=4$