In `[Fe(CN)_5(NO)]^(2-)`, Fe has `+2` state. It cannot be dicided by

Answer

To solve the question regarding the oxidation state of iron in the complex ion \([Fe(CN)_5(NO)]^{2-}\), we need to analyze the options provided and determine which methods cannot be used to ascertain that iron is in the +2 oxidation state.

### Step-by-Step Solution:

1. **Identify the Oxidation State of Iron**:
- In the complex \([Fe(CN)_5(NO)]^{2-}\), we need to determine the oxidation state of Fe.
- The overall charge of the complex is -2. The cyanide ion (CN) has a charge of -1 and there are five CN ligands, contributing a total charge of -5.
- The nitrosyl (NO) ligand is neutral in this context.
- Let the oxidation state of Fe be \(x\). The equation can be set up as follows:
\[ x + 5(-1) + 0 = -2 \]
\[ x - 5 = -2 \implies x = +3 \]
- However, the question states that Fe is in the +2 oxidation state, which we will accept for the purpose of this question.

2. **Evaluate Each Option**:
- **Option A: Magnetic Measurement**:
- Magnetic measurements can be used to determine the number of unpaired electrons in the d-orbitals, which can indicate the oxidation state. Since Fe in +2 state has 4 unpaired electrons, this method can help identify the oxidation state.
- **Conclusion**: This option can help determine the oxidation state.

- **Option B: Colligative Properties**:
- Colligative properties depend on the number of solute particles in a solution and are not influenced by the identity of the solute. Since we are dealing with a complex and not a simple salt, this method cannot determine the oxidation state of Fe.
- **Conclusion**: This option cannot help determine the oxidation state.

- **Option C: Color**:
- The color of a compound can provide some information about its oxidation state, but in the case of Fe, both +2 and +3 oxidation states can give similar colors (green). Thus, color alone cannot definitively indicate the oxidation state.
- **Conclusion**: This option cannot help determine the oxidation state.

- **Option D: Hybridization**:
- Hybridization is related to the geometry and bonding in the complex but does not directly provide information about the oxidation state of the metal ion.
- **Conclusion**: This option cannot help determine the oxidation state.

3. **Final Conclusion**:
- Based on the evaluations, options B (Colligative Properties) and C (Color) are the methods that cannot be used to determine that Fe has a +2 oxidation state in the complex \([Fe(CN)_5(NO)]^{2-}\).

### Answer:
The correct answer is **Option B and Option C**.