The coordination environment of Ca²⁺ ion in its complex with EDTA⁴⁻ is :

Solution

Chemistry ma’am · 4 steps

Count the donor atoms of EDTA first: six donors around one ion means an octahedron.

1. Donor atoms. EDTA⁴⁻ has 2 nitrogen atoms and 4 carboxylate oxygen atoms that can each give a lone pair. So it is a hexadentate ligand.
2. Coordination number. One EDTA⁴⁻ wraps around the Ca²⁺ ion and binds through all six donors at once. That gives coordination number 6 and the 1 : 1 chelate [Ca(EDTA)]²⁻.
3. Shape. Six donor atoms around one centre arrange themselves at the corners of an octahedron. Coordination number 4 would give tetrahedral or square planar, so those cannot fit six donors.
4. So. The Ca²⁺ ion sits in an octahedral environment, option (b).

The idea to keep. For a chelating ligand, count its donor atoms to get the coordination number, then match the shape: 6 means octahedral, 4 means tetrahedral or square planar.

Answer from the NTA final answer key. Solution by PrepWiser.