Among the following which are ambidentate ligands?
(i) `NO_2^(-)`
(ii) `NO_3^(-)`
(iii) `C_2O_4^(2-)`
(iv) `SCN^(-)`

Options

A. (a) (i) and (iv)
B. (b) (i) and (ii)
C. (c) (ii) and (iii)
D. (d) (iii) and (iv)

Explanation

To determine which of the given ligands are ambidentate, we need to analyze each ligand to see if it can coordinate through two different atoms.

### Step-by-Step Solution:

1. **Identify the Ligands**:
The ligands provided are:
- (i) `NO_2^(-)`
- (ii) `NO_3^(-)`
- (iii) `C_2O_4^(2-)`
- (iv) `SCN^(-)`

2. **Analyze `NO_2^(-)`**:
- The nitrite ion (`NO_2^(-)`) has a nitrogen atom and two oxygen atoms.
- The nitrogen can donate a lone pair, and one of the oxygen atoms carries a negative charge and can also donate a lone pair.
- Therefore, `NO_2^(-)` can coordinate through both nitrogen and oxygen, making it an ambidentate ligand.

3. **Analyze `NO_3^(-)`**:
- The nitrate ion (`NO_3^(-)`) has a nitrogen atom bonded to three oxygen atoms.
- However, the nitrogen does not have a lone pair available for donation, and only one of the oxygen atoms can donate a pair of electrons.
- Thus, `NO_3^(-)` cannot coordinate through two different atoms and is not an ambidentate ligand.

4. **Analyze `C_2O_4^(2-)`**:
- The oxalate ion (`C_2O_4^(2-)`) has two carbon atoms and four oxygen atoms.
- Although it has multiple oxygen atoms, they are all similar in terms of their ability to donate electrons (they are all oxygen).
- Therefore, `C_2O_4^(2-)` does not qualify as an ambidentate ligand since it does not coordinate through two different types of atoms.

5. **Analyze `SCN^(-)`**:
- The thiocyanate ion (`SCN^(-)`) consists of a sulfur atom and a nitrogen atom.
- The sulfur atom has a negative charge and can donate a lone pair, while the nitrogen atom can also donate a lone pair.
- Since it can coordinate through both sulfur and nitrogen, `SCN^(-)` is an ambidentate ligand.

### Conclusion:
The ambidentate ligands among the given options are:
- (i) `NO_2^(-)`
- (iv) `SCN^(-)`

### Summary of Results:
- Ambidentate Ligands: `NO_2^(-)` and `SCN^(-)`
- Non-ambidentate Ligands: `NO_3^(-)` and `C_2O_4^(2-)`