How many EDTA (ethylenediaminetetraacetic acid) molecules are required to make an octahedral complex with a Ca^2+ ion?

Coordination Compounds PYQ — JEE Main 2006 · Shift 0 · Q11 with Solution

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Correct answer: C

Identify the denticity of EDTA

EDTA (ethylenediaminetetraacetic acid) acts as a hexadentate ligand.

This means one EDTA molecule can donate 6 lone pairs to the metal ion.
Coordination number for an octahedral complex

An octahedral complex requires 6 coordination sites around the metal ion.
Apply this to $Ca^{2+}$

Since one EDTA molecule already provides all 6 donor atoms, only one EDTA molecule is needed to form an octahedral complex with $Ca^{2+}$ .

The complex formed is of the type: $[Ca(\text{EDTA})]^{2-}$ (representation may vary depending on protonation state).
Evaluate the options
- A: Six $\rightarrow$ Incorrect
- B: Three $\rightarrow$ Incorrect
- C: One $\rightarrow$ Correct
- D: Two $\rightarrow$ Incorrect
Final Answer

The required number of EDTA molecules is: $\boxed{1}$ So the correct option is C.