Coordination number of central metal ion in [Cu(H₂O)₄en]²⁺ is

6

The coordination number (CN) of a metal ion in a complex can be defined as the number of ligand donor atoms to which the metal is directly bonded.

In [Cu(H₂O)₄en]²⁺ ,

x + 4(0) + 1(0) = 2

x = +2

Coordination number of Cu²⁺ is 6 because en is a bidentate ligand and four H₂O molecules are monodentate ligands.