Read the passage given below and answer the following questions :
The crystal field theory (CFT) is an electrostatic model which considers the metal-ligand bond to be ionic arising purely from electrostatic interactions between the metal ion and the ligand. Ligands are treated as point charges in case of anions or dipoles in case of neutral molecules. The five d orbitals in an isolated gaseous metal atom/ion have same energy, i.e., they are degenerate. This degeneracy is maintained if a spherically symmetrical field of negative charges surrounds the metal atom/ ion. However, when this negative field is due to ligands (either anions or the negative ends of dipolar molecules like `NH_(3)` and `H_(2)O`) in a complex, it becomes asymmetrical and the degeneracy of the d orbitals is lifted. It results in splitting of the d orbitals.
A chelating agent has two or more than two donor atoms to bind to a single metal ion. Which of the following is not a chelating agent ?

Options

A. thiosulphato
B. oxalato
C. glycinato
D. ethane-1,2-diamine

Explanation

To determine which of the given options is not a chelating agent, we need to analyze the structures of the ligands mentioned and see if they have two or more donor atoms that can bind to a single metal ion.

### Step-by-Step Solution:

1. **Understanding Chelating Agents**:
- A chelating agent is a ligand that has two or more donor atoms capable of forming coordinate bonds with a single metal ion. This results in the formation of a stable ring structure.

2. **Analyzing Ethane-1,2-diamine**:
- Structure: NH2-CH2-CH2-NH2
- It has two amine groups (NH2) that can donate electron pairs to a metal ion.
- Therefore, it can form a stable five-membered ring when it coordinates to a metal ion.
- **Conclusion**: Ethane-1,2-diamine is a chelating agent.

3. **Analyzing Glycinate**:
- Structure: NH2-CH2-COO^-
- It has an amine group (NH2) and a carboxylate group (COO^-), both of which can act as donor atoms.
- This ligand can also form a stable five-membered ring when it coordinates to a metal ion.
- **Conclusion**: Glycinate is a chelating agent.

4. **Analyzing Oxalate**:
- Structure: (COO^-)2
- Oxalate has two carboxylate groups that can donate electron pairs to a metal ion.
- It can form a stable five-membered ring with a metal ion.
- **Conclusion**: Oxalate is a chelating agent.

5. **Analyzing Thiosulfate**:
- Structure: S2O3^2-
- Thiosulfate has two oxygen atoms that can act as donor atoms, but it does not form a stable ring structure when it coordinates to a metal ion.
- The potential ring formed is a four-membered ring, which is generally unstable due to angle strain.
- **Conclusion**: Thiosulfate is not a chelating agent; it is an ambidentate ligand.

### Final Answer:
The ligand that is not a chelating agent is **Thiosulfate**.