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

The correct answer is Option (4) → 6

The coordination number is the number of donor atoms bonded to the metal, not the number of ligands.

In \( \ce{[Cu(H2O)4en]^{2+}} \):
4 \( \ce{H2O} \) (unidentate) → 4 × 1 = 4 donor atoms
1 en, \( \ce{H2NCH2CH2NH2} \) (didentate) → 1 × 2 = 2 donor atoms
Coordination number = 4 + 2 = 6

NCERT (2026-27 edition):
Definitions of Some Important Terms Pertaining to Coordination Compounds – “… When a ligand is bound to a metal ion through a single donor atom, as with Cl^–, H₂O or NH₃, the ligand is said to be unidentate. When a ligand can bind through two donor atoms as in H₂NCH₂CH₂NH₂ (ethane-1,2-diamine) or C₂O₄^2– (oxalate), the ligand is said to be didentate and when several donor atoms are present in a single ligand as in N(CH₂CH₂NH₂)₃, the ligand is said to be polydentate.”