The oxidation number that iron does not exhibit in its common compounds or in its elemental state is:

Options

A. 0
B. `+1`
C. `+2`
D. `+3`

Answer

To determine the oxidation number that iron does not exhibit in its common compounds or in its elemental state, we can follow these steps:

### Step 1: Identify the Element and Its Atomic Number
Iron is represented by the symbol Fe and has an atomic number of 26.

### Step 2: Determine the Electron Configuration
Iron's electron configuration can be derived from its atomic number. The electron configuration is:
- The previous noble gas is Argon (Ar), which has the configuration [Ne]3s²3p⁶.
- Therefore, the electron configuration for iron is:
\[ [Ar] 4s^2 3d^6 \]

### Step 3: Understand Oxidation States
In its elemental form, iron has an oxidation state of 0. When it forms compounds, iron can exhibit various oxidation states, primarily +2 and +3.

### Step 4: Analyze Common Oxidation States
- The +2 oxidation state (Fe²⁺) occurs when iron loses its two 4s electrons.
- The +3 oxidation state (Fe³⁺) occurs when iron loses two 4s electrons and one 3d electron, resulting in a stable half-filled 3d subshell (3d⁵).

### Step 5: Identify the Oxidation State Not Exhibited
The oxidation state that iron does not exhibit in its common compounds or elemental state is +1. This is because:
- The removal of one electron from the stable 4s² configuration is energetically unfavorable due to the stability of the filled 4s subshell.
- Therefore, iron does not commonly exhibit the +1 oxidation state.

### Conclusion
The oxidation number that iron does not exhibit in its common compounds or in its elemental state is **+1**.

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