Consider the following molecules .
`A`:Anti -pyridine -2-carboxaldoxime
`B`:syn pyridine -2-carboaxaldoxime
`C`: nickel -dimethyl glyoximate
`D` : o-nitrophenol
`E` : p-nitrophenol
`F` : p-salicylaldehyde
In which case chelate formation occurs ? .

Options

A. `A,B`
B. `B,C`
C. `C,F`
D. `C` only

Explanation

To determine in which of the given molecules chelate formation occurs, we need to analyze each molecule for the possibility of intramolecular hydrogen bonding, which is essential for chelation.

### Step-by-Step Solution:

1. **Analyze Anti-pyridine-2-carboxaldoxime (A)**:
- Structure: In this molecule, the carboxaldoxime group is positioned in such a way that it can form a hydrogen bond with the nitrogen atom of the pyridine ring.
- Conclusion: A six-membered chelate ring is formed due to this intramolecular hydrogen bonding. **Chelation occurs.**

2. **Analyze Syn-pyridine-2-carboxaldoxime (B)**:
- Structure: Here, the carboxaldoxime group is on the same side as the pyridine nitrogen.
- Conclusion: The spatial arrangement does not allow for effective intramolecular hydrogen bonding. **No chelation occurs.**

3. **Analyze Nickel-dimethylglyoximate (C)**:
- Structure: This molecule has two oxime groups that can coordinate with the nickel atom, forming two chelate rings.
- Conclusion: Intramolecular hydrogen bonding occurs, leading to chelation. **Chelation occurs.**

4. **Analyze o-Nitrophenol (D)**:
- Structure: In this molecule, the hydroxyl (OH) group can form a hydrogen bond with the nitro (NO2) group due to their proximity.
- Conclusion: This results in the formation of a stable chelate ring. **Chelation occurs.**

5. **Analyze p-Nitrophenol (E)**:
- Structure: The hydroxyl (OH) group and the nitro (NO2) group are positioned far apart.
- Conclusion: There is no possibility for intramolecular hydrogen bonding. **No chelation occurs.**

6. **Analyze p-Salicylaldehyde (F)**:
- Structure: Similar to p-nitrophenol, the OH and CHO groups are also far apart.
- Conclusion: There is no effective intramolecular hydrogen bonding. **No chelation occurs.**

### Summary of Chelation:
- **Chelation occurs in molecules A (Anti-pyridine-2-carboxaldoxime), C (Nickel-dimethylglyoximate), and D (o-Nitrophenol).**
- **No chelation occurs in molecules B (syn-pyridine-2-carboxaldoxime), E (p-nitrophenol), and F (p-salicylaldehyde).**

### Final Answer:
Chelate formation occurs in molecules A, C, and D.

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