`[Mn(CO)_(4)NO]` is diamagnetic because:

Options

A. Mn metal is diamagnetiic in free state
B. Mn is in +1 oxidation state in this complex
C. No is present as positive ligand
D. All of these

Explanation

To determine why the compound `[Mn(CO)4NO]` is diamagnetic, we need to analyze the oxidation state of manganese and the electronic configuration of the compound. Here’s a step-by-step breakdown of the solution:

### Step 1: Determine the oxidation state of manganese in `[Mn(CO)4NO]`.
- **CO (carbon monoxide)** is a neutral ligand, contributing 0 to the oxidation state.
- **NO (nitrosyl)** can exist in different oxidation states, but in this case, it is assumed to be in the -1 oxidation state.
- Let the oxidation state of manganese be \( x \).

The equation for the oxidation state can be set up as:
\[ x + 4(0) + (-1) = 0 \implies x - 1 = 0 \implies x = +1 \]

### Step 2: Write the electronic configuration of manganese in the +1 oxidation state.
- Manganese (Mn) has an atomic number of 25, with the ground state electronic configuration:
\[ \text{Mn: } [Ar] 4s^2 3d^5 \]
- In the +1 oxidation state, one electron is removed from the 4s orbital:
\[ \text{Mn}^{+1}: [Ar] 4s^1 3d^5 \]

### Step 3: Analyze the electron configuration.
- In the +1 oxidation state, the electron configuration is \( 4s^1 3d^5 \).
- The 3d subshell has 5 electrons, which are distributed as follows:
- Each of the 5 d electrons is unpaired in the absence of strong field ligands.

### Step 4: Determine the effect of the ligands (CO and NO).
- **CO** is a strong field ligand and causes pairing of electrons.
- **NO** in this case acts as a strong field ligand as well.
- The presence of these strong field ligands will lead to the pairing of the 3d electrons.

### Step 5: Write the paired electron configuration after ligand interaction.
- When the strong field ligands (CO and NO) are present, the 3d electrons will pair up:
- The new configuration will be \( 3d^6 \) (all paired) and \( 4s^0 \).

### Step 6: Conclusion about the magnetic property.
- Since all electrons are paired in the final configuration, the compound `[Mn(CO)4NO]` is **diamagnetic**.

### Final Answer:
`[Mn(CO)4NO]` is diamagnetic because in the +1 oxidation state, the strong field ligands (CO and NO) cause the 3d electrons to pair up, resulting in no unpaired electrons.

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